U.S. patent application number 15/540189 was filed with the patent office on 2018-07-19 for method for producing acetic acid.
This patent application is currently assigned to DAICEL CORPORATION. The applicant listed for this patent is DAICEL CORPORATION. Invention is credited to Masahiko SHIMIZU.
Application Number | 20180201563 15/540189 |
Document ID | / |
Family ID | 62838238 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180201563 |
Kind Code |
A1 |
SHIMIZU; Masahiko |
July 19, 2018 |
METHOD FOR PRODUCING ACETIC ACID
Abstract
It is intended to provide a method capable of lowering a formic
acid concentration in product acetic acid by a simple approach. The
method for producing acetic acid according to the present invention
comprises at least one step selected from a step that satisfies the
following operating conditions (i) and a step that satisfies the
following operating conditions (ii) in an acetic acid production
process: (i) operating conditions involving a hydrogen partial
pressure of less than 500 kPa (absolute pressure), a carbon dioxide
partial pressure of less than 70 kPa (absolute pressure), and an
operating temperature of more than 175.degree. C.; and (ii)
operating conditions involving a hydrogen partial pressure of not
more than 5 kPa (absolute pressure), a carbon dioxide partial
pressure of less than 20 kPa (absolute pressure), and an operating
temperature of more than 100.degree. C.
Inventors: |
SHIMIZU; Masahiko;
(Himeji-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAICEL CORPORATION |
Osaka-shi, Osaka |
|
JP |
|
|
Assignee: |
DAICEL CORPORATION
Osaka-shi, Osaka
JP
|
Family ID: |
62838238 |
Appl. No.: |
15/540189 |
Filed: |
May 25, 2017 |
PCT Filed: |
May 25, 2017 |
PCT NO: |
PCT/JP2017/019575 |
371 Date: |
June 27, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02P 20/10 20151101;
B01D 3/009 20130101; B01D 15/361 20130101; C07C 51/44 20130101;
C07C 51/12 20130101; B01D 3/143 20130101; C07C 51/445 20130101;
C07C 51/12 20130101; C07C 53/08 20130101; C07C 51/44 20130101; C07C
53/08 20130101 |
International
Class: |
C07C 51/12 20060101
C07C051/12; C07C 51/44 20060101 C07C051/44; B01D 3/00 20060101
B01D003/00; B01D 3/14 20060101 B01D003/14; B01D 15/36 20060101
B01D015/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2017 |
JP |
2017-006647 |
Mar 2, 2017 |
JP |
2017-039391 |
Claims
1. A method for producing acetic acid, comprising at least one step
selected from a step that satisfies the following operating
conditions (i) and a step that satisfies the following operating
conditions (ii) in an acetic acid production process: (i) operating
conditions involving a hydrogen partial pressure of less than 500
kPa (absolute pressure), a carbon dioxide partial pressure of less
than 70 kPa (absolute pressure), and an operating temperature of
more than 175.degree. C. and not more than 250.degree. C.; and (ii)
operating conditions involving a hydrogen partial pressure of not
more than 5 kPa (absolute pressure), a carbon dioxide partial
pressure of less than 20 kPa (absolute pressure), and an operating
temperature of more than 100.degree. C. and not more than
250.degree. C., wherein the acetic acid production process has at
least one distillation step, a column top fraction of a
distillation column in the at least one distillation step is
recycled to the step that satisfies the operating conditions (i)
and/or the step that satisfies the operating conditions (ii), the
step to which the column top fraction of a distillation column is
recycled is a reaction step and/or an evaporation step or a
distillation step positioned upstream from the distillation step
associated with the distillation column, and the step that
satisfies the operating conditions (i) or the step that satisfies
the operating conditions (ii) decomposes formic acid in the column
top fraction.
2. The method for producing acetic acid according to claim 1,
wherein the operating conditions (ii) involve a hydrogen partial
pressure of not more than 1 kPa (absolute pressure) and a carbon
dioxide partial pressure of less than 2 kPa (absolute
pressure).
3. The method for producing acetic acid according to claim 1,
wherein the method has a reaction step that satisfies the operating
conditions (i).
4. The method for producing acetic acid according to claim 3,
wherein a reaction mixture liquid in the reaction step has an
acetic acid concentration of not less than 30% by mass and a formic
acid concentration of not more than 102 ppm by mass.
5. The method for producing acetic acid according to claim 3,
wherein a reaction mixture liquid in the reaction step has an
acetic acid concentration of 50 to 90% by mass, a metal catalyst
concentration (in terms of the metal) of 200 to 10000 ppm by mass,
a methyl iodide concentration of 1 to 20% by mass, an ionic iodide
concentration of 1 to 25% by mass, a water concentration of 0.1 to
15% by mass, a methyl acetate concentration of 0.1 to 30% by mass,
and a formic acid concentration of not more than 102 ppm by
mass.
6. The method for producing acetic acid according to claim 1,
wherein the method has an evaporation step or a distillation step
that satisfies the operating conditions (ii).
7. The method for producing acetic acid according to claim 6,
wherein a charging mixture for an evaporator in the evaporation
step has an acetic acid concentration of 50 to 90% by mass, a metal
catalyst concentration (in terms of the metal) of 200 to 10000 ppm
by mass, a methyl iodide concentration of 1 to 20% by mass, an
ionic iodide concentration of 1 to 25% by mass, a water
concentration of 0.1 to 15% by mass, a methyl acetate concentration
of 0.1 to 30% by mass, and a formic acid concentration of not more
than 10000 ppm by mass.
8. The method for producing acetic acid according to claim 6,
wherein a charging mixture for a distillation column in the
distillation step that satisfies the operating conditions (ii) has
an acetic acid concentration of not less than 30% by mass and a
formic acid concentration of not less than 5 ppm by mass.
9. The method for producing acetic acid according to claim 6,
wherein a charging mixture for a distillation column in the
distillation step that satisfies the operating conditions (ii) has
an acetic acid concentration of 40 to 85% by mass, a methyl iodide
concentration of 2 to 50% by mass, a water concentration of 0.2 to
20% by mass, a methyl acetate concentration of 0.2 to 50% by mass,
and a formic acid concentration of 5 to 10000 ppm by mass.
10. The method for producing acetic acid according to claim 6,
wherein a charging mixture for a distillation column in the
distillation step that satisfies the operating conditions (ii) has
an acetic acid concentration of 80 to 99.9% by mass, a methyl
iodide concentration of 0.01 to 16% by mass, a water concentration
of 0.05 to 18% by mass, a methyl acetate concentration of 0.01 to
16% by mass, and a formic acid concentration of 5 to 10000 ppm by
mass.
11. The method for producing acetic acid according to claim 6,
wherein a charging mixture for a distillation column in the
distillation step that satisfies the operating conditions (ii) has
an acetic acid concentration of 99.1 to 99.999% by mass and a
formic acid concentration of 5 to 9000 ppm by mass.
12. The method for producing acetic acid according to claim 1,
wherein the acetic acid production process has a carbonylation
reaction step of reacting methanol with carbon monoxide to produce
acetic acid, an evaporation step of separating the reaction mixture
obtained in the carbonylation reaction step into a vapor stream and
a residual liquid stream, and a lower boiling point component
removal step of separating the vapor stream by distillation into an
overhead stream rich in lower boiling point component and a first
acetic acid stream rich in acetic acid, or wherein the acetic acid
production process further has at least one of the following steps
(a)-(d) in addition to the carbonylation reaction step, the
evaporation step, and the lower boiling point component removal
step: (a) a dehydration step of separating the first acetic acid
stream by distillation into an overhead stream rich in water and a
second acetic acid stream more enriched with acetic acid than the
first acetic acid stream, (b) a higher boiling point component
removal step of separating the first acetic acid stream or the
second acetic acid stream by distillation into a bottom stream rich
in higher boiling point component and a third acetic acid stream
more enriched with acetic acid than the acetic acid stream before
the distillation, (c) an adsorptive removal step of treating the
first acetic acid stream, the second acetic acid stream, or the
third acetic acid stream with an ion exchange resin to obtain a
fourth acetic acid stream, and (d) a product step of distilling the
first acetic acid stream, the second acetic acid stream, the third
acetic acid stream or the fourth acetic acid stream to obtain a
fifth acetic acid stream more enriched with acetic acid than the
acetic acid stream before the distillation.
13. The method for producing acetic acid according to claim 12,
wherein the carbonylation reaction step satisfies the operating
conditions (i).
14. The method for producing acetic acid according to claim 12,
wherein at least one step selected from the evaporation step, the
lower boiling point component removal step, the dehydration step,
the higher boiling point component removal step, and the product
step satisfies the operating conditions (ii).
15. The method for producing acetic acid according to claim 1,
wherein a retention time in the step that satisfies the operating
conditions (i) or the step that satisfies the operating conditions
(ii) is not less than 1 minute.
16. The method for producing acetic acid according to claim 1,
wherein a process solution having a formic acid concentration of
not less than 10 ppm by mass is recycled to a step that satisfies
operating conditions involving a hydrogen partial pressure of less
than 500 kPa (absolute pressure), a carbon dioxide partial pressure
of less than 70 kPa (absolute pressure), and an operating
temperature of more than 100.degree. C.
17-18. (canceled)
19. The method for producing acetic acid according to claim 1,
wherein the column top fraction to be recycled is a column top
fraction of a distillation column that a charging mixture for the
distillation column has an acetic acid concentration of 80 to
99.999% by mass.
20. The method for producing acetic acid according to claim 1,
wherein the operating conditions (i) involves a hydrogen partial
pressure of not less than 1 and less than 500 kPa (absolute
pressure), and the operating conditions (ii) involves a carbon
dioxide partial pressure of less than 12 kPa (absolute pressure)
and an operating temperature of 106.degree. C. to 250.degree.
C.
21. The method for producing acetic acid according to claim 1,
wherein a retention time in the step that satisfies the operating
conditions (i) or the step that satisfies the operating conditions
(ii) is not less than 1 minute and not more than 2 hours.
22. The method for producing acetic acid according to claim 1,
wherein the method has a distillation step that satisfies the
operating conditions (ii), and a charging mixture for a
distillation column in the distillation step that satisfies the
operating condition (ii) has a formic acid concentration of 5 to
1000 ppm by mass.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing
acetic acid. The present application claims the priorities of
Japanese Patent Application No. 2017-006647 filed in Japan on Jan.
18, 2017 and Japanese Patent Application No. 2017-039391 filed in
Japan on Mar. 2, 2017, the contents of which are incorporated
herein by reference in their entirety.
BACKGROUND ART
[0002] A carbonylation process of a methanol method is known as an
industrial method for producing acetic acid. In this process, for
example, methanol and carbon monoxide are reacted in the presence
of a catalyst in a reaction vessel to produce acetic acid. The
reaction mixture is evaporated in an evaporator, and the vapor
phase is purified in a lower boiling point component removal column
and subsequently in a dehydration column so that product acetic
acid is prepared. Alternatively, product acetic acid is prepared
via a higher boiling point component removal column subsequent to
the dehydration column, and further, a product column.
[0003] In such an acetic acid production process, formic acid is
produced as a by-product in the reaction vessel. The minimum amount
of formic acid is favorable because the formic acid reduces the
purity of product acetic acid. Patent Literatures 1 and 2 disclose
that: formic acid is formed through the reaction of carbon monoxide
with water; and therefore, the formic acid concentration in product
acetic acid can be lowered by controlling a water concentration in
a reaction medium to a low level. However, there is the problem
that a catalyst becomes unstable if the water concentration in the
reaction medium is decreased.
CITATION LIST
Patent Literature
[0004] Patent Literature 1: U.S. Patent Application Publication No.
2008/0293966
[0005] Patent Literature 2: U.S. Patent Application Publication No.
2008/0293967
SUMMARY OF INVENTION
Technical Problem
[0006] An object of the present invention is to provide a method
capable of lowering a formic acid concentration in product acetic
acid by a simple approach.
Solution to Problem
[0007] In order to attain the object, the present inventors have
conducted diligent studies to discover a mechanism underlying
formic acid formation and consequently gained the findings that:
more than a little formic acid is formed, mainly, in a reaction
vessel, an evaporator, and a lower boiling point component removal
column where hydrogen and carbon dioxide are present; at a higher
hydrogen partial pressure and carbon dioxide partial pressure, more
formic acid is formed; at a higher temperature, formic acid
formation is suppressed; the presence of equilibrium reaction of
H.sub.2+CO.sub.2HHCOOH is predicted from these; etc. Accordingly,
the present inventors have conducted further studies and found
that: for suppressing formic acid formation, it is desirable to
maintain a low hydrogen partial pressure, a low carbon dioxide
partial pressure, and a high temperature; formic acid can be
decomposed by recycling a process solution containing the formic
acid to a reaction vessel, an evaporator, or a distillation column
and maintaining a low hydrogen partial pressure, a low carbon
dioxide partial pressure, and a high temperature; because formic
acid has a lower boiling point than that of acetic acid and is
therefore concentrated at the column top of each distillation
column, a column top fraction of the distillation column is
recycled to the reaction system or a distillation column positioned
upstream from the distillation column so that formic acid can be
decomposed; etc. The present invention is based on these findings
and has been completed through further studies.
[0008] Specifically, the present invention provides a method for
producing acetic acid, comprising at least one step selected from a
step that satisfies the following operating conditions (i) and a
step that satisfies the following operating conditions (ii) in an
acetic acid production process:
[0009] (i) operating conditions involving a hydrogen partial
pressure of less than 500 kPa (absolute pressure), a carbon dioxide
partial pressure of less than 70 kPa (absolute pressure), and an
operating temperature of more than 175.degree. C.; and
[0010] (ii) operating conditions involving a hydrogen partial
pressure of not more than 5 kPa (absolute pressure), a carbon
dioxide partial pressure of less than 20 kPa (absolute pressure),
and an operating temperature of more than 100.degree. C.
[0011] The operating conditions (ii) may involve a hydrogen partial
pressure of not more than 1 kPa (absolute pressure) and a carbon
dioxide partial pressure of less than 2 kPa (absolute
pressure).
[0012] The method for producing acetic acid according to the
present invention may have a reaction step that satisfies the
operating conditions (i). In this case, a reaction mixture liquid
in the reaction step may have an acetic acid concentration of not
less than 30% by mass and a formic acid concentration of not more
than 102 ppm by mass. Also, the reaction mixture liquid in the
reaction step may have an acetic acid concentration of 50 to 90% by
mass, a metal catalyst concentration (in terms of the metal) of 200
to 10000 ppm by mass, a methyl iodide concentration of 1 to 20% by
mass, an ionic iodide concentration of 1 to 25% by mass, a water
concentration of 0.1 to 15% by mass, a methyl acetate concentration
of 0.1 to 30% by mass, and a formic acid concentration of not more
than 102 ppm by mass.
[0013] The method for producing acetic acid according to the
present invention may have an evaporation step or a distillation
step that satisfies the operating conditions (ii). A charging
mixture for an evaporator in the evaporation step may have an
acetic acid concentration of 50 to 90% by mass, a metal catalyst
concentration (in terms of the metal) of 200 to 10000 ppm by mass,
a methyl iodide concentration of 1 to 20% by mass, an ionic iodide
concentration of 1 to 25% by mass, a water concentration of 0.1 to
15% by mass, a methyl acetate concentration of 0.1 to 30% by mass,
and a formic acid concentration of not more than 10000 ppm by mass.
Also, a charging mixture for a distillation column in the
distillation step may have an acetic acid concentration of not less
than 30% by mass and a formic acid concentration of not less than 5
ppm by mass. Furthermore, a charging mixture for a distillation
column in the distillation step may have an acetic acid
concentration of 40 to 85% by mass, a methyl iodide concentration
of 2 to 50% by mass, a water concentration of 0.2 to 20% by mass, a
methyl acetate concentration of 0.2 to 50% by mass, and a formic
acid concentration of 5 to 10000 ppm by mass. Moreover, a charging
mixture for a distillation column in the distillation step may have
an acetic acid concentration of 80 to 99.9% by mass, a methyl
iodide concentration of 0.01 to 16% by mass, a water concentration
of 0.05 to 18% by mass, a methyl acetate concentration of 0.01 to
16% by mass, and a formic acid concentration of 5 to 10000 ppm by
mass. Also, a charging mixture for a distillation column in the
distillation step may have an acetic acid concentration of 99.1 to
99.999% by mass and a formic acid concentration of 5 to 9000 ppm by
mass.
[0014] In the method for producing acetic acid according to the
present invention, the acetic acid production process may have a
carbonylation reaction step of reacting methanol with carbon
monoxide to produce acetic acid, an evaporation step of separating
the reaction mixture obtained in the carbonylation reaction step
into a vapor stream and a residual liquid stream, a lower boiling
point component removal step of separating the vapor stream by
distillation into an overhead stream rich in lower boiling point
component and a first acetic acid stream rich in acetic acid, or
the acetic acid production process may further have at least one of
the following steps (a)-(d) in addition to the carbonylation
reaction step, the evaporation step, and the lower boiling point
component removal step:
(a) a dehydration step of separating the first acetic acid stream
by distillation into an overhead stream rich in water and a second
acetic acid stream more enriched with acetic acid than the first
acetic acid stream, (b) a higher boiling point component removal
step of separating the first acetic acid stream or the second
acetic acid stream by distillation into a bottom stream rich in
higher boiling point component and a third acetic acid stream more
enriched with acetic acid than the acetic acid stream before the
distillation, (c) an adsorptive removal step of treating the first
acetic acid stream, the second acetic acid stream, or the third
acetic acid stream with an ion exchange resin to obtain a fourth
acetic acid stream, and
[0015] (d) a product step of distilling the first acetic acid
stream, the second acetic acid stream, the third acetic acid stream
or the fourth acetic acid stream to obtain a fifth acetic acid
stream more enriched with acetic acid than the acetic acid stream
before the distillation.
[0016] In this case, the carbonylation reaction step may satisfy
the operating conditions (i). Also, at least one step selected from
the evaporation step, the lower boiling point component removal
step, the dehydration step, the higher boiling point component
removal step, and the product step may satisfy the operating
conditions (ii).
[0017] In the method for producing acetic acid according to the
present invention, it is preferred that a retention time in the
step that satisfies the operating conditions (i) or the step that
satisfies the operating conditions (ii) should be not less than 1
minute.
[0018] In the method for producing acetic acid according to the
present invention, a process solution having a formic acid
concentration of not less than 10 ppm by mass may be recycled to a
step that satisfies operating conditions involving a hydrogen
partial pressure of less than 500 kPa (absolute pressure), a carbon
dioxide partial pressure of less than 70 kPa (absolute pressure),
and an operating temperature of more than 100.degree. C.
[0019] In the method for producing acetic acid according to the
present invention, the acetic acid production process may have at
least one distillation step, and a column top fraction of a
distillation column in the at least one distillation step may be
recycled to the step that satisfies the operating conditions (i)
and/or the step that satisfies the operating conditions (ii). In
this case, the step to which the column top fraction of a
distillation column is recycled may be the reaction step and/or the
evaporation step or a distillation step positioned upstream from
the distillation step associated with the distillation column.
Advantageous Effects of Invention
[0020] According to the present invention, formic acid formation
can be suppressed, or formed formic acid can be efficiently
decomposed, because of having a step that satisfies particular
operating conditions. Therefore, a formic acid concentration in
product acetic acid can be simply lowered.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is an acetic acid production flow diagram showing one
embodiment of the present invention.
[0022] FIG. 2 is a schematic flow diagram showing one example of an
acetaldehyde separation and removal system.
[0023] FIG. 3 is a schematic flow diagram showing another example
of the acetaldehyde separation and removal system.
[0024] FIG. 4 is a schematic flow diagram showing a further
alternative example of the acetaldehyde separation and removal
system.
[0025] FIG. 5 is a schematic flow diagram showing a further
alternative example of the acetaldehyde separation and removal
system.
[0026] DESCRIPTION OF EMBODIMENTS
[0027] The method for producing acetic acid according to the
present invention comprises at least one step selected from a step
that satisfies the following operating conditions (i) and a step
that satisfies the following operating conditions (ii) in an acetic
acid production process:
[0028] (i) operating conditions involving a hydrogen partial
pressure of less than 500 kPa (absolute pressure), a carbon dioxide
partial pressure of less than 70 kPa (absolute pressure), and an
operating temperature of more than 175.degree. C.; and
[0029] (ii) operating conditions involving a hydrogen partial
pressure of not more than 5 kPa (absolute pressure), a carbon
dioxide partial pressure of less than 20 kPa (absolute pressure),
and an operating temperature of more than 100.degree. C.
[0030] In the step that satisfies such operating conditions, formic
acid formation is effectively suppressed, while formic acid in a
feeding liquid for the step is efficiently decomposed. This is
presumably because equilibrium reaction of H.sub.2+CO.sub.2HCOOH
exists, and this equilibrium is shifted to the left side under the
operating conditions described above. The step that satisfies the
operating conditions may be any of a reaction step, an evaporation
step, a distillation step, and the like.
[0031] In the present specification, the "hydrogen partial
pressure" and the "carbon dioxide partial pressure" mean partial
pressures of these components in a gaseous phase portion in an
apparatus or equipment (a reactor, an evaporator, a distillation
column, etc.) for use in the step. In the distillation column, the
partial pressures in a gaseous phase portion of at least one plate
(e.g., a bottom plate, a feeding plate, or an uppermost plate) can
fall within the ranges described above. It is preferred that the
partial pressures in a gaseous phase portion of each plate from the
feeding plate to the uppermost plate should fall within the ranges
described above. It is more preferred that the partial pressures in
a gaseous phase portion of each plate from the bottom plate to the
uppermost plate should fall within the ranges described above. The
"operating temperature" means the temperature of a liquid phase
portion or a gaseous phase portion in an apparatus or equipment (a
reactor, an evaporator, a distillation column, etc.) for use in the
step. In the distillation column, the temperature of a liquid phase
portion or a gaseous phase portion of at least one plate (e.g., a
bottom plate, a feeding plate, or an uppermost plate) can fall
within the range described above. It is preferred that the
temperature of a liquid phase portion or a gaseous phase portion of
each plate from the feeding plate to the uppermost plate should
fall within the range described above. It is more preferred that
the temperature of a liquid phase portion or a gaseous phase
portion of each plate from the bottom plate to the uppermost plate
should fall within the range described above.
[0032] In the operating conditions (i), the hydrogen partial
pressure (absolute pressure) can be less than 500 kPa and is
preferably not more than 400 kPa, more preferably not more than 300
kPa, further preferably not more than 200 kPa, particularly
preferably not more than 150 kPa. Although the lower limit of the
hydrogen partial pressure (absolute pressure) is 0 kPa, the
hydrogen partial pressure (absolute pressure) may be more than 1
kPa (or more than 5 kPa). The carbon dioxide partial pressure
(absolute pressure) can be less than 70 kPa and is preferably not
more than 60 kPa, more preferably not more than 50 kPa, further
preferably not more than 40 kPa, particularly preferably not more
than 30 kPa. The lower limit of the carbon dioxide partial pressure
(absolute pressure) is 0 kPa, but may be 2 kPa (or 20 kPa). The
operating temperature can be a temperature of more than 175.degree.
C. and is preferably not less than 178.degree. C., more preferably
not less than 181.degree. C., further preferably not less than
184.degree. C. The upper limit of the operating temperature is, for
example, 250.degree. C., preferably 230.degree. C., more preferably
200.degree. C.
[0033] In the operating conditions (ii), the hydrogen partial
pressure (absolute pressure) can be not more than 5 kPa and is
preferably not more than 4 kPa, more preferably not more than 3
kPa, further preferably not more than 2 kPa, particularly
preferably not more than 1 kPa. The lower limit of the hydrogen
partial pressure (absolute pressure) is 0 kPa. The carbon dioxide
partial pressure (absolute pressure) can be less than 20 kPa and is
preferably not more than 18 kPa, more preferably not more than 16
kPa, further preferably not more than 14 kPa, particularly
preferably not more than 12 kPa. The lower limit of the carbon
dioxide partial pressure (absolute pressure) is 0 kPa. The
operating temperature can be a temperature of more than 100.degree.
C. and is preferably not less than 102.degree. C., more preferably
not less than 104.degree. C., further preferably not less than
106.degree. C., particularly preferably not less than 112.degree.
C. The upper limit of the operating temperature is, for example,
250.degree. C., preferably 200.degree. C., more preferably
175.degree. C.
[0034] In the operating conditions (ii), the hydrogen partial
pressure (absolute pressure) may be not more than 1 kPa, and the
carbon dioxide partial pressure (absolute pressure) may be less
than 2 kPa. In this case, the upper limit of the hydrogen partial
pressure (absolute pressure) is preferably 0.9 kPa, more preferably
0.8 kPa. The lower limit of the hydrogen partial pressure (absolute
pressure) is 0 kPa. The upper limit of the carbon dioxide partial
pressure (absolute pressure) is preferably 1.8 kPa, more preferably
1.5 kPa, further preferably 1.0 kPa, particularly preferably 0.5
kPa. The lower limit of the carbon dioxide partial pressure
(absolute pressure) is 0 kPa.
[0035] Examples of the step that satisfies the operating conditions
(i) include a reaction step. In this case, it is preferred that a
reaction mixture liquid in the reaction step should have an acetic
acid concentration of not less than 30% by mass (e.g., 30 to 90% by
mass) and a formic acid concentration of not more than 102 ppm by
mass (0 to 102 ppm by mass). Further preferably, the reaction
mixture liquid in the reaction step has an acetic acid
concentration of 50 to 90% by mass (e.g., 60 to 80% by mass), a
metal catalyst concentration (in terms of the metal) of 200 to 5000
ppm by mass (e.g., 400 to 2000 ppm by mass), a methyl iodide
concentration of 1 to 20% by mass (e.g., 5 to 15% by mass), an
ionic iodide concentration of 1 to 25% by mass (e.g., 5 to 20% by
mass), a water concentration of 0.1 to 15% by mass (e.g., 0.8 to
10% by mass), a methyl acetate concentration of 0.1 to 30% by mass
(e.g., 1 to 10% by mass), and a formic acid concentration of not
more than 85 ppm by mass (0 to 85 ppm by mass).
[0036] Examples of the step that satisfies the operating conditions
(ii) include an evaporation step and a distillation step. In the
evaporation step that satisfies the operating conditions (ii), a
charging mixture for an evaporator may have an acetic acid
concentration of 50 to 90% by mass (e.g., 60 to 80% by mass), a
metal catalyst concentration (in terms of the metal) of 200 to 5000
ppm by mass (e.g., 400 to 2000 ppm by mass), a methyl iodide
concentration of 1 to 20% by mass (e.g., 5 to 15% by mass), an
ionic iodide concentration of 1 to 25% by mass (e.g., 5 to 20% by
mass), a water concentration of 0.1 to 15% by mass (e.g., 0.8 to
10% by mass), a methyl acetate concentration of 0.1 to 30% by mass
(e.g., 1 to 10% by mass), and a formic acid concentration of not
more than 10000 ppm by mass (e.g., 0 to 1000 ppm by mass,
preferably 10 to 500 ppm by mass, further preferably 15 to 200 ppm
by mass, particularly preferably 20 to 100 ppm by mass).
[0037] In the distillation step that satisfies the operating
conditions (ii), a charging mixture for a distillation column may
have an acetic acid concentration of not less than 30% by mass
(e.g., 30 to 99.999% by mass) and a formic acid concentration of
not less than 5 ppm by mass (e.g., 5 to 10000 ppm by mass). Also,
in the distillation step, a charging mixture for a distillation
column may have an acetic acid concentration of 40 to 85% by mass
(e.g., 50 to 75% by mass), a methyl iodide concentration of 2 to
50% by mass (e.g., 5 to 30% by mass), a water concentration of 0.2
to 20% by mass (e.g., 1 to 15% by mass), a methyl acetate
concentration of 0.2 to 50% by mass (e.g., 2 to 30% by mass), and a
formic acid concentration of 5 to 10000 ppm by mass (e.g., 10 to
1000 ppm by mass, preferably 10 to 500 ppm by mass, further
preferably 15 to 200 ppm by mass, particularly preferably 20 to 100
ppm by mass). Furthermore, in the distillation step, a charging
mixture for a distillation column may have an acetic acid
concentration of 80 to 99.9% by mass (e.g., 90 to 99.9% by mass,
preferably 93 to 99% by mass), a methyl iodide concentration of
0.01 to 16% by mass (e.g., 0.1 to 8% by mass, preferably 0.2 to 5%
by mass), a water concentration of 0.05 to 18% by mass (e.g., 0.1
to 8% by mass, preferably 0.2 to 5% by mass), a methyl acetate
concentration of 0.01 to 16% by mass (e.g., 0.1 to 8% by mass,
preferably 0.2 to 5% by mass), and a formic acid concentration of 5
to 10000 ppm by mass (e.g., 10 to 1000 ppm by mass, preferably 10
to 500 ppm by mass, further preferably 15 to 200 ppm by mass,
particularly preferably 20 to 100 ppm by mass). Moreover, in the
distillation step, a charging mixture for a distillation column may
have an acetic acid concentration of 99.1 to 99.999% by mass and a
formic acid concentration of 5 to 9000 ppm by mass (e.g., 10 to
1000 ppm by mass, preferably 10 to 500 ppm by mass, further
preferably 15 to 200 ppm by mass, particularly preferably 20 to 100
ppm by mass).
[0038] In the method for producing acetic acid, the acetic acid
production process may have a carbonylation reaction step of
reacting methanol with carbon monoxide to produce acetic acid, an
evaporation step of separating the reaction mixture obtained in the
carbonylation reaction step into a vapor stream and a residual
liquid stream, a lower boiling point component removal step of
separating the vapor stream by distillation into an overhead stream
rich in lower boiling point component and a first acetic acid
stream rich in acetic acid, and a dehydration step of separating
the first acetic acid stream by distillation into an overhead
stream rich in water and a second acetic acid stream more enriched
with acetic acid than the first acetic acid stream. Alternatively,
in addition to the steps, the acetic acid production process may
further have at least one of the following steps (a)-(d) in
addition to the carbonylation reaction step, the evaporation step,
and the lower boiling point component removal step:
(a) a dehydration step of separating the first acetic acid stream
by distillation into an overhead stream rich in water and a second
acetic acid stream more enriched with acetic acid than the first
acetic acid stream, (b) a higher boiling point component removal
step of separating the first acetic acid stream or the second
acetic acid stream by distillation into a bottom stream rich in
higher boiling point component and a third acetic acid stream more
enriched with acetic acid than the acetic acid stream before the
distillation, (c) an adsorptive removal step of treating the first
acetic acid stream, the second acetic acid stream, or the third
acetic acid stream with an ion exchange resin to obtain a fourth
acetic acid stream, and (d) a product step of distilling the first
acetic acid stream, the second acetic acid stream, the third acetic
acid stream or the fourth acetic acid stream to obtain a fifth
acetic acid stream more enriched with acetic acid than the acetic
acid stream before the distillation.
[0039] The carbonylation reaction step may satisfy the operating
conditions (i). Also, at least one step selected from the
evaporation step, the lower boiling point component removal step,
the dehydration step, the higher boiling point component removal
step, and the product step (preferably the lower boiling point
component removal step, further preferably the lower boiling point
component removal step and the dehydration step, alternatively the
evaporation step and the lower boiling point component removal
step, particularly preferably the evaporation step, lower boiling
point component removal step, and the dehydration step) may satisfy
the operating conditions (ii).
[0040] In the method for producing acetic acid according to the
present invention, it is preferred that a retention time in the
step that satisfies the operating conditions (i) or (ii) should be
not less than 1 minute (e.g., not less than 5 minutes,
particularly, not less than 10 minutes). The upper limit of the
retention time is, for example, 2 hours, preferably 1 hour. Formic
acid contained in the system can be securely decomposed by
retention for the predetermined time under the operating conditions
(i) or (ii).
[0041] In the method for producing acetic acid according to the
present invention, a process solution having a formic acid
concentration of not less than 10 ppm by mass (e.g., 10 to 10000
ppm by mass, preferably 15 to 1000 ppm by mass, further preferably
20 to 200 ppm by mass) may be recycled to the step that satisfies
the operating conditions (i) and/or the step that satisfies the
operating conditions (ii) (e.g., the reaction step, the evaporation
step, the lower boiling point component removal step, or the
dehydration step). Formic acid in such a process solution can be
efficiently decomposed by recycling the process solution to the
step.
[0042] In the method for producing acetic acid according to the
present invention, the acetic acid production process may have at
least one distillation step, and a column top fraction of a
distillation column in the at least one distillation step may be
recycled to the step that satisfies the operating conditions (i)
and/or the step that satisfies the operating conditions (ii).
Examples of the step that satisfies the operating conditions (i)
and the step that satisfies the operating conditions (ii) include
the reaction step, the evaporation step, the lower boiling point
component removal step, and the dehydration step. In this case, it
is preferred that the step to which the column top fraction of a
distillation column is recycled should be the reaction step or
should be the evaporation step or a distillation step positioned
upstream from the distillation step associated with the
distillation column. Because formic acid has a lower boiling point
than that of acetic acid and is therefore concentrated at the
column top, a column top fraction of the distillation column is
recycled to the step that satisfies the operating conditions (i)
and/or the step that satisfies the operating conditions (ii) so
that formic acid in the column top fraction can be efficiently
decomposed.
[0043] Hereinafter, one embodiment of the present invention will be
described. FIG. 1 is one example of an acetic acid production flow
diagram (carbonylation process of a methanol method) showing one
embodiment of the present invention. An acetic acid production
apparatus associated with this acetic acid production flow has a
reaction vessel 1, an evaporator 2, a distillation column 3, a
decanter 4, a distillation column 5, a distillation column 6, an
ion exchange resin column 7, a scrubber system 8, an acetaldehyde
separation and removal system 9, condensers 1a, 2a, 3a, 5a, and 6a,
a heat exchanger 2b, reboilers 3b, 5b, and 6b, lines 11 to 56, and
a pump 57 and is configured to be capable of continuously producing
acetic acid. In the method for producing acetic acid according to
the present embodiment, a reaction step, an evaporation step (flash
step), a first distillation step, a second distillation step, a
third distillation step, and an adsorptive removal step are
performed in the reaction vessel 1, the evaporator 2, the
distillation column 3, the distillation column 5, the distillation
column 6, and the ion exchange resin column 7, respectively. The
first distillation step is also referred to as a lower boiling
point component removal step, the second distillation step is also
referred to as a dehydration step, and the third distillation step
is also referred to as a higher boiling point component removal
step. In the present invention, the steps are not limited to those
described above and may exclude, particularly, equipment of the
distillation column 5, the distillation column (higher boiling
point component removal column) 6, the ion exchange resin column 7,
the acetaldehyde separation and removal system 9 (acetaldehyde
removal column, etc.). As mentioned later, a product column may be
disposed downstream of the ion exchange resin column 7.
[0044] The reaction vessel 1 is a unit for performing the reaction
step. This reaction step is a step for continuously producing
acetic acid through a reaction (methanol carbonylation reaction)
represented by the chemical formula (1) given below. In a steady
operation state of the acetic acid production apparatus, for
example, a reaction mixture under stirring with a stirrer is
present in the reaction vessel 1. The reaction mixture contains
methanol and carbon monoxide which are raw materials, a metal
catalyst, a co-catalyst, water, a production target acetic acid,
and various by-products, and a liquid phase and a gaseous phase are
in equilibrium.
CH.sub.3OH+CO.fwdarw.CH.sub.3COOH (1)
[0045] The raw materials in the reaction mixture are methanol in a
liquid state and carbon monoxide in a gaseous state. Methanol is
continuously fed at a predetermined flow rate to the reaction
vessel 1 from a methanol reservoir (not shown) through the line 11.
Carbon monoxide is continuously fed at a predetermined flow rate to
the reaction vessel 1 from a carbon monoxide reservoir (not shown)
through the line 12. The carbon monoxide is not necessarily
required to be pure carbon monoxide and may contain, for example,
other gases such as nitrogen, hydrogen, carbon dioxide, and oxygen,
in a small amount (e.g., not more than 5% by mass, preferably not
more than 1% by mass).
[0046] The metal catalyst in the reaction mixture promotes the
carbonylation reaction of methanol, and, for example, a rhodium
catalyst or an iridium catalyst can be used. For example, a rhodium
complex represented by the chemical formula [Rh(CO).sub.2I.sub.2]
can be used as the rhodium catalyst. For example, an iridium
complex represented by the chemical formula [Ir(CO).sub.3I.sub.3]
can be used as the iridium catalyst. A metal complex catalyst is
preferred as the metal catalyst. The concentration (in terms of the
metal) of the catalyst in the reaction mixture is, for example, 200
to 10000 ppm by mass, preferably 300 to 5000 ppm by mass, further
preferably 400 to 2000 ppm by mass, with respect to the whole
liquid phase (reaction mixture liquid) of the reaction mixture.
[0047] The co-catalyst is an iodide for assisting the action of the
catalyst mentioned above, and, for example, methyl iodide or an
ionic iodide is used. The methyl iodide can exhibit the effect of
promoting the catalytic effect of the catalyst mentioned above. The
concentration of the methyl iodide is, for example, 1 to 20% by
mass (preferably 5 to 15% by mass) with respect to the whole liquid
phase of the reaction mixture. The ionic iodide is an iodide that
generates iodide ions in a reaction solution (particularly, an
ionic metal iodide) and can exhibit the effect of stabilizing the
catalyst mentioned above and the effect of suppressing side
reaction. Examples of the ionic iodide include alkali metal iodides
such as lithium iodide, sodium iodide, and potassium iodide. The
concentration of the ionic iodide in the reaction mixture is, for
example, 1 to 25% by mass, preferably 5 to 20% by mass, with
respect to the whole liquid phase of the reaction mixture. In
addition, when an iridium catalyst or the like is used, for
example, a ruthenium compound or an osmium compound can be used as
a co-catalyst. The amount of these compounds to be used as the
total amount is, for example 0.1 to 30 moles (in terms of metal),
preferably 0.5 to 15 moles (in terms of metal) based on 1 mole of
iridium (in terms of metal).
[0048] Water in the reaction mixture is a component necessary for
generating acetic acid in the reaction mechanism of the methanol
carbonylation reaction and is also a component necessary for
solubilizing a water-soluble component in the reaction system. The
concentration of water in the reaction mixture is, for example, 0.1
to 15% by mass, preferably 0.8 to 10% by mass, further preferably 1
to 6% by mass, particularly preferably 1.5 to 4% by mass, with
respect to the whole liquid phase of the reaction mixture. The
water concentration is preferably not more than 15% by mass for
pursuing efficient acetic acid production by reducing energy
required for the removal of water in the course of purification of
acetic acid. In order to control the water concentration, water may
be continuously fed at a predetermined flow rate to the reaction
vessel 1.
[0049] The acetic acid in the reaction mixture includes acetic acid
fed in advance into the reaction vessel 1 before operation of the
acetic acid production apparatus, and acetic acid generated as a
main product of the methanol carbonylation reaction. Such acetic
acid can function as a solvent in the reaction system. The
concentration of the acetic acid in the reaction mixture is, for
example, 50 to 90% by mass, preferably 60 to 80% by mass, with
respect to the whole liquid phase of the reaction mixture.
[0050] Examples of the main by-products contained in the reaction
mixture include methyl acetate. This methyl acetate may be
generated through the reaction between acetic acid and methanol.
The concentration of the methyl acetate in the reaction mixture is,
for example, 0.1 to 30% by mass, preferably 1 to 10% by mass, with
respect to the whole liquid phase of the reaction mixture. Another
example of the by-products contained in the reaction mixture
includes hydrogen iodide. This hydrogen iodide is inevitably
generated under the reaction mechanism of the methanol
carbonylation reaction in the case where the catalyst or the
co-catalyst as mentioned above is used. The concentration of the
hydrogen iodide in the reaction mixture is, for example, 0.01 to 2%
by mass with respect to the whole liquid phase of the reaction
mixture. Other examples of the by-products include hydrogen,
methane, carbon dioxide, acetaldehyde, crotonaldehyde, 2-ethyl
crotonaldehyde, dimethyl ether, alkanes, formic acid, propionic
acid, and alkyl iodides such as hexyl iodide and decyl iodide.
Also, the reaction mixture may contain a metal, such as iron,
nickel, chromium, manganese, or molybdenum, generated by the
corrosion of the apparatus (hereinafter, also referred to as a
"corroded metal"), and other metals such as cobalt, zinc, and
copper. The corroded metal and other metals are also collectively
referred to as a "corroded metal, etc.". The total content of these
impurities such as by-products and corroded metals is, for example,
1 ppm by mass to 1% by mass with respect to the whole liquid phase
of the reaction mixture. Thus, the process solution in this acetic
acid production process may contain, for example, approximately 1
ppm by mass to 1% by mass in total of the impurities. The
concentration of the formic acid in the reaction mixture is, for
example, 0 to 102 ppm by mass, preferably 0 to 85 ppm by mass,
further preferably 0 to 50 ppm by mass, with respect to the whole
liquid phase of the reaction mixture.
[0051] In the reaction vessel 1 where the reaction mixture as
described above is present, the reaction temperature is set to, for
example, 150 to 250.degree. C. The reaction pressure as the total
pressure is set to, for example, 2.0 to 3.5 MPa (absolute
pressure), and the carbon monoxide partial pressure is set to, for
example, 0.4 to 1.8 MPa (absolute pressure), preferably 0.6 to 1.5
MPa (absolute pressure).
[0052] The vapor of a gaseous phase portion in the reaction vessel
1 during apparatus operation contains, for example, carbon
monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen,
methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid,
dimethyl ether, methanol, acetaldehyde, formic acid, and propionic
acid. This vapor can be withdrawn from the reaction vessel 1
through the line 13. The internal pressure of the reaction vessel 1
can be controlled by the adjustment of the amount of the vapor
withdrawn, and, for example, the internal pressure of the reaction
vessel 1 is kept constant. The vapor withdrawn from the reaction
vessel 1 is introduced to the condenser 1a.
[0053] The condenser 1a separates the vapor from the reaction
vessel 1 into a condensate portion and a gaseous portion by cooling
and partial condensation. The condensate portion contains, for
example, methyl iodide, hydrogen iodide, water, methyl acetate,
acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid,
and propionic acid and is introduced to the reaction vessel 1 from
the condenser 1a through the line 14 and recycled. The gaseous
portion contains, for example, carbon monoxide, hydrogen, methane,
carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide,
water, methyl acetate, acetic acid, dimethyl ether, methanol,
acetaldehyde, and formic acid and is fed to the scrubber system 8
from the condenser 1a through the line 15. In the scrubber system
8, useful components (e.g., methyl iodide, water, methyl acetate,
and acetic acid) are separated and recovered from the gaseous
portion from the condenser 1a. In this separation and recovery, a
wet method that is performed using an absorbing liquid for
capturing the useful components in the gaseous portion is utilized
in the present embodiment. An absorption solvent containing at
least acetic acid and/or methanol is preferred as the absorbing
liquid. The absorbing liquid may contain methyl acetate. For
example, a condensate portion of a vapor from the distillation
column 6 mentioned later can be used as the absorbing liquid. In
the separation and recovery, a pressure swing adsorption method may
be used. The separated and recovered useful components (e.g.,
methyl iodide) are introduced to the reaction vessel 1 from the
scrubber system 8 through the recycle line 48 and recycled. A gas
after the capturing of the useful components is discarded through
the line 49. The gas discharged from the line 49 can be used as a
CO source to be introduced to the bottom part of the evaporator 2
mentioned later or the residual liquid stream recycle lines 18 and
19. As for treatment in the scrubber system 8 and subsequent
recycle to the reaction vessel 1 and discarding, the same holds
true for gaseous portions described later that are fed to the
scrubber system 8 from other condensers. For the production method
of the present invention, it is preferred to have a scrubber step
of separating offgas from the process into a stream rich in carbon
monoxide and a stream rich in acetic acid by absorption treatment
with an absorption solvent containing at least acetic acid.
[0054] In the reaction vessel 1 during apparatus operation, as
mentioned above, acetic acid is continuously produced. The reaction
mixture containing such acetic acid is continuously withdrawn at a
predetermined flow rate from the reaction vessel 1 and introduced
to the next evaporator 2 through the line 16.
[0055] In the present invention, it is preferred that the reaction
step using the reaction vessel 1 should satisfy the operating
conditions (i) involving a hydrogen partial pressure of less than
500 kPa (absolute pressure), a carbon dioxide partial pressure of
less than 70 kPa (absolute pressure), and an operating temperature
of more than 175.degree. C. In this case, the hydrogen partial
pressure (absolute pressure) can be less than 500 kPa and is
preferably not more than 400 kPa, more preferably not more than 300
kPa, further preferably not more than 200 kPa, particularly
preferably not more than 150 kPa. Although the lower limit of the
hydrogen partial pressure (absolute pressure) is 0 kPa, the
hydrogen partial pressure (absolute pressure) may be more than 1
kPa (or more than 5 kPa). The carbon dioxide partial pressure
(absolute pressure) can be less than 70 kPa and is preferably not
more than 60 kPa, more preferably not more than 50 kPa, further
preferably not more than 40 kPa, particularly preferably not more
than 30 kPa. The lower limit of the carbon dioxide partial pressure
(absolute pressure) is 0 kPa, but may be 2 kPa (or 20 kPa). The
operating temperature can be a temperature of more than 175.degree.
C. and is preferably not less than 178.degree. C., more preferably
not less than 181.degree. C., further preferably not less than
184.degree. C. The upper limit of the operating temperature is, for
example, 250.degree. C., preferably 230.degree. C., more preferably
200.degree. C. The reaction step using the reaction vessel 1
satisfies the operating conditions (i), whereby formic acid
formation in the reaction vessel 1 is suppressed. Furthermore, when
a liquid containing formic acid is introduced to the reaction
vessel 1, the formic acid is efficiently decomposed.
[0056] The evaporator 2 is a unit for performing the evaporation
step (flash step). This evaporation step is a step for separating
the reaction mixture continuously introduced to the evaporator 2
through the line 16 (reaction mixture feed line), into a vapor
stream (volatile phase) and a residual liquid stream (low volatile
phase) by partial evaporation. The evaporation may be caused by
reducing the pressure without heating the reaction mixture, or the
evaporation may be caused by reducing the pressure while heating
the reaction mixture. In the evaporation step, the temperature of
the vapor stream is, for example, 100 to 260.degree. C., preferably
120 to 200.degree. C., and the temperature of the residual liquid
stream is, for example, 80 to 200.degree. C., preferably 100 to
180.degree. C. The internal pressure of the evaporator is, for
example, 50 to 1000 kPa (absolute pressure). The ratio between the
vapor stream and the residual liquid stream to be separated in the
evaporation step is, for example, 10/90 to 50/50 (vapor
stream/residual liquid stream) in terms of a mass ratio. The vapor
generated in this step contains, for example, methyl iodide,
hydrogen iodide, water, methyl acetate, acetic acid, dimethyl
ether, methanol, acetaldehyde, formic acid, and propionic acid and
is continuously withdrawn to the line 17 (vapor stream discharge
line) from the evaporator 2. A portion of the vapor stream
withdrawn from the evaporator 2 is continuously introduced to the
condenser 2a, and another portion of the vapor stream is
continuously introduced to the next distillation column 3 through
the line 21. The acetic acid concentration of the vapor stream is,
for example, 50 to 85% by mass, preferably 55 to 75% by mass. The
residual liquid stream generated in this step contains, for
example, the catalyst and the co-catalyst (methyl iodide, lithium
iodide, etc.) contained in the reaction mixture, and water, methyl
acetate, acetic acid, formic acid, and propionic acid remaining
without being volatilized in this step, and is continuously
introduced to the heat exchanger 2b from the evaporator 2 through
the line 18 using the pump 57. The heat exchanger 2b cools the
residual liquid stream from the evaporator 2. The cooled residual
liquid stream is continuously introduced to the reaction vessel 1
from the heat exchanger 2b through the line 19 and recycled. The
line 18 and the line 19 are collectively referred to as residual
liquid stream recycle lines. The acetic acid concentration of the
residual liquid stream is, for example, 55 to 90% by mass,
preferably 60 to 85% by mass.
[0057] The condenser 2a separates the vapor stream from the
evaporator 2 into a condensate portion and a gaseous portion by
cooling and partial condensation. The condensate portion contains,
for example, methyl iodide, hydrogen iodide, water, methyl acetate,
acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid,
and propionic acid and is introduced to the reaction vessel 1 from
the condenser 2a through the lines 22 and 23 and recycled. The
gaseous portion contains, for example, carbon monoxide, hydrogen,
methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen
iodide, water, methyl acetate, acetic acid, dimethyl ether,
methanol, acetaldehyde, and formic acid and is fed to the scrubber
system 8 from the condenser 2a through the lines 20 and 15. Since
the reaction to produce acetic acid in the reaction step mentioned
above is an exothermic reaction, a portion of heat accumulated in
the reaction mixture is transferred to the vapor generated from the
reaction mixture in the evaporation step (flash step). The
condensate portion generated by the cooling of this vapor in the
condenser 2a is recycled to the reaction vessel 1. Specifically, in
this acetic acid production apparatus, heat generated through the
methanol carbonylation reaction is efficiently removed in the
condenser 2a.
[0058] In the present invention, it is preferred that the
evaporation step using the evaporator 2 should satisfy the
operating conditions (ii) involving a hydrogen partial pressure of
not more than 5 kPa (absolute pressure), a carbon dioxide partial
pressure of less than 20 kPa (absolute pressure), and an operating
temperature of more than 100.degree. C. In this case, the hydrogen
partial pressure (absolute pressure) is preferably not more than 4
kPa, more preferably not more than 3 kPa, further preferably not
more than 1 kPa, particularly preferably not more than 0.8 kPa. The
lower limit of the hydrogen partial pressure (absolute pressure) is
0 kPa. The carbon dioxide partial pressure (absolute pressure) is
preferably not more than 12 kPa, more preferably 8 kPa, further
preferably not more than 3 kPa, particularly preferably not more
than 1 kPa. The lower limit of the carbon dioxide partial pressure
(absolute pressure) is 0 kPa. The operating temperature is
preferably not less than 112.degree. C., more preferably not less
than 120.degree. C., further preferably not less than 130.degree.
C. The upper limit of the operating temperature is, for example,
260.degree. C., preferably 200.degree. C., more preferably
180.degree. C. (or 170.degree. C. or 160.degree. C.).
[0059] In the evaporation step that satisfies the operating
conditions (ii), the charging mixture for the evaporator 2 may have
an acetic acid concentration of, for example, 50 to 90% by mass
(preferably 60 to 80% by mass), a metal catalyst concentration (in
terms of the metal) of, for example, 200 to 10000 ppm by mass
(preferably 300 to 5000 ppm by mass, further preferably 400 to 2000
ppm by mass), a methyl iodide concentration of, for example, 1 to
20% by mass (preferably 5 to 15% by mass), an ionic iodide
concentration of, for example, 1 to 25% by mass (preferably 5 to
20% by mass), a water concentration of, for example, 0.1 to 15% by
mass (preferably 0.8 to 10% by mass), a methyl acetate
concentration of, for example, 0.1 to 30% by mass (preferably 1 to
10% by mass), and a formic acid concentration of, for example, not
more than 10000 ppm by mass (preferably 0 to 1000 ppm by mass, more
preferably 10 to 500 ppm by mass, further preferably 15 to 200 ppm
by mass, particularly preferably 20 to 100 ppm by mass). The
evaporation step using the evaporator 2 satisfies the operating
conditions, whereby formic acid formation in the evaporator 2 is
suppressed. Furthermore, when a liquid containing formic acid is
introduced to the evaporator 2, the formic acid is efficiently
decomposed.
[0060] The distillation column 3 is a unit for performing the first
distillation step and serves as the so-called lower boiling point
component removal column in the present embodiment. The first
distillation step is the step of subjecting the vapor stream
continuously introduced to the distillation column 3 to
distillation treatment to separate and remove lower boiling point
components. More specifically, in the first distillation step, the
vapor stream is separated by distillation into an overhead stream
rich in at least one lower boiling point component selected from
methyl iodide and acetaldehyde, and an acetic acid stream rich in
acetic acid. The distillation column 3 consists of, for example, a
distillation column such as a plate column or a packed column. In
the case of adopting a plate column as the distillation column 3,
the theoretical number of plates thereof is, for example, 5 to 50,
and the reflux ratio is, for example, 0.5 to 3000 according to the
theoretical number of plates. In the inside of the distillation
column 3, the column top pressure is set to, for example, 80 to 160
kPa (gauge pressure), and the column bottom pressure is higher than
the column top pressure and is set to, for example, 85 to 180 kPa
(gauge pressure). In the inside of the distillation column 3, the
column top temperature is, for example, a temperature of lower than
the boiling point of acetic acid at the set column top pressure and
is set to 90 to 130.degree. C., and the column bottom temperature
is, for example, a temperature of not less than the boiling point
of acetic acid at the set column bottom pressure and is set to 120
to 165.degree. C. (preferably 125 to 160.degree. C.).
[0061] The vapor stream from the evaporator 2 is continuously
introduced to the distillation column 3 through the line 21. From
the column top of the distillation column 3, a vapor as the
overhead stream is continuously withdrawn to the line 24. From the
column bottom of the distillation column 3, a bottom fraction is
continuously withdrawn to the line 25. 3b denotes a reboiler. From
the height position between the column top and the column bottom of
the distillation column 3, the acetic acid stream (first acetic
acid stream; liquid) as a side stream is continuously withdrawn
through the line 27.
[0062] The vapor withdrawn from the column top of the distillation
column 3 contains a larger amount of components having a lower
boiling point (lower boiling point components) than that of acetic
acid as compared with the bottom fraction and the side stream from
the distillation column 3 and contains, for example, methyl iodide,
hydrogen iodide, water, methyl acetate, dimethyl ether, methanol,
acetaldehyde, and formic acid. This vapor also contains acetic
acid. Such a vapor is continuously introduced to the condenser 3a
through the line 24.
[0063] The condenser 3a separates the vapor from the distillation
column 3 into a condensate portion and a gaseous portion by cooling
and partial condensation. The condensate portion contains, for
example, methyl iodide, hydrogen iodide, water, methyl acetate,
acetic acid, dimethyl ether, methanol, acetaldehyde, and formic
acid and is continuously introduced to the decanter 4 from the
condenser 3a through the line 28. The condensate portion introduced
to the decanter 4 is separated into an aqueous phase (upper phase)
and an organic phase (methyl iodide phase; lower phase). The
aqueous phase contains water and, for example, methyl iodide,
hydrogen iodide, methyl acetate, acetic acid, dimethyl ether,
methanol, acetaldehyde, and formic acid. The organic phase
contains, for example, methyl iodide and, for example, hydrogen
iodide, water, methyl acetate, acetic acid, dimethyl ether,
methanol, acetaldehyde, and formic acid. In the present embodiment,
a portion of the aqueous phase is refluxed to the distillation
column 3 through the line 29, and another portion of the aqueous
phase is introduced to the reaction vessel 1 through the lines 29,
30, and 23 and recycled. A portion of the organic phase is
introduced to the reaction vessel 1 through the lines 31 and 23 and
recycled. Another portion of the organic phase and/or a remaining
portion of the aqueous phase is introduced to the acetaldehyde
separation and removal system 9 through the lines 31 and 50 and/or
the lines 30 and 51.
[0064] In the present invention, it is preferred that the
distillation step using the distillation column (lower boiling
point component removal column) 3 should satisfy the operating
conditions (ii) involving a hydrogen partial pressure of not more
than 5 kPa (absolute pressure), a carbon dioxide partial pressure
of less than 20 kPa (absolute pressure), and an operating
temperature of more than 100.degree. C. In this case, the hydrogen
partial pressure (absolute pressure) is preferably not more than 4
kPa, more preferably not more than 3 kPa, further preferably not
more than 1 kPa. The lower limit of the hydrogen partial pressure
(absolute pressure) is 0 kPa. The carbon dioxide partial pressure
(absolute pressure) is preferably not more than 12 kPa, more
preferably not more than 8 kPa, further preferably not more than 3
kPa, particularly preferably not more than 1 kPa. The lower limit
of the carbon dioxide partial pressure (absolute pressure) is 0
kPa. The operating temperature is preferably not less than
112.degree. C., more preferably not less than 114.degree. C. The
upper limit of the operating temperature is, for example,
165.degree. C., preferably 160.degree. C., more preferably
150.degree. C. (or 140.degree. C. or 130.degree. C.).
[0065] In the case where the distillation step using the
distillation column (lower boiling point component removal column)
3 satisfies the operating conditions (ii), the charging mixture for
the distillation column 3 may have an acetic acid concentration of
not less than 30% by mass (e.g., 30 to 99.999% by mass) and a
formic acid concentration of not less than 5 ppm by mass (e.g., 5
to 10000 ppm by mass). Also, the charging mixture for the
distillation column 3 has an acetic acid concentration of
preferably 40 to 85% by mass (e.g., 50 to 85% by mass), further
preferably 50 to 75% by mass (e.g., 55 to 75% by mass), a methyl
iodide concentration of preferably 2 to 50% by mass (e.g., 5 to 30%
by mass), a water concentration of preferably 0.2 to 20% by mass
(e.g., 1 to 15% by mass), a methyl acetate concentration of
preferably 0.2 to 50% by mass (e.g., 2 to 30% by mass), and a
formic acid concentration of preferably 5 to 10000 ppm by mass
(e.g., 10 to 1000 ppm by mass, more preferably 10 to 500 ppm by
mass, particularly, 15 to 200 ppm by mass, in particular, 20 to 100
ppm by mass). The distillation step using the distillation column 3
satisfies the operating conditions (ii), whereby formic acid
formation in the distillation column 3 is suppressed. In addition,
when a liquid containing formic acid is fed to the distillation
column 3, the formic acid is efficiently decomposed.
[0066] In the acetaldehyde separation and removal step using the
acetaldehyde separation and removal system 9, acetaldehyde
contained in the organic phase and/or the aqueous phase is
separated and removed by a method known in the art, for example,
distillation, extraction, or a combination thereof. The separated
acetaldehyde is discharge to the outside of the apparatus through
the line 53. The useful components (e.g., methyl iodide) contained
in the organic phase and/or the aqueous phase are recycled to the
reaction vessel 1 through the lines 52 and 23 and reused.
[0067] FIG. 2 is a schematic flow diagram showing one example of
the acetaldehyde separation and removal system. According to this
flow, in the case of treating, for example, the organic phase in
the acetaldehyde separation and removal step, the organic phase is
fed to a distillation column (first acetaldehyde removal column) 91
through a line 101 and separated by distillation into an overhead
stream rich in acetaldehyde (line 102) and a residual liquid stream
rich in methyl iodide (line 103). The overhead stream is condensed
in a condenser 91a. A portion of the condensate is refluxed to the
column top of the distillation column 91 (line 104), and the
remaining portion of the condensate is fed to an extraction column
92 (line 105). The condensate fed to the extraction column 92 is
subjected to extraction treatment with water introduced from a line
109. The extract obtained by the extraction treatment is fed to a
distillation column (second acetaldehyde removal column) 93 through
a line 107 and separated by distillation into an overhead stream
rich in acetaldehyde (line 112) and a residual liquid stream rich
in water (line 113). Then, the overhead stream rich in acetaldehyde
is condensed in a condenser 93a. A portion of the condensate is
refluxed to the column top of the distillation column 93 (line
114), and the remaining portion of the condensate is discharged to
the outside of the system (line 115). The residual liquid stream
rich in methyl iodide, which is a bottom fraction of the first
acetaldehyde removal column 91, a raffinate rich in methyl iodide
(line 108) obtained in the extraction column 92, and the residual
liquid stream rich in water, which is a bottom fraction of the
second acetaldehyde removal column 93 are recycled to the reaction
vessel 1 through the lines 103, 111, and 113, respectively, or
recycled to an appropriate area of the process and reused. For
example, the raffinate rich in methyl iodide, obtained in the
extraction column 92, can be recycled to the distillation column 91
through a line 110. The liquid from the line 113 is usually
discharged to the outside as water discharge. A gas that has not
been condensed in the condenser 91a or 93a (line 106 or 116) is
subjected to absorption treatment in the scrubber system 8 or
discarded.
[0068] According to the flow of FIG. 2, in the case of treating the
aqueous phase in the acetaldehyde separation and removal step, for
example, the aqueous phase is fed to the distillation column (first
acetaldehyde removal column) 91 through the line 101 and separated
by distillation into an overhead stream rich in acetaldehyde (line
102) and a residual liquid stream rich in water (line 103). The
overhead stream is condensed in the condenser 91a. A portion of the
condensate is refluxed to the column top of the distillation column
91 (line 104), and the remaining portion of the condensate is fed
to the extraction column 92 (line 105). The condensate fed to the
extraction column 92 is subjected to extraction treatment with
water introduced from the line 109. The extract obtained by the
extraction treatment is fed to the distillation column (second
acetaldehyde removal column) 93 through the line 107 and separated
by distillation into an overhead stream rich in acetaldehyde (line
112) and a residual liquid stream rich in water (line 113). Then,
the overhead stream rich in acetaldehyde is condensed in the
condenser 93a. A portion of the condensate is refluxed to the
column top of the distillation column 93 (line 114), and the
remaining portion of the condensate is discharged to the outside of
the system (line 115). The residual liquid stream rich in water,
which is a bottom fraction of the first acetaldehyde removal column
91, a raffinate rich in methyl iodide (line 108) obtained in the
extraction column 92, and the residual liquid stream rich in water,
which is a bottom fraction of the second acetaldehyde removal
column 93 are recycled to the reaction vessel 1 through the lines
103, 111, and 113, respectively, or recycled to an appropriate area
of the process and reused. For example, the raffinate rich in
methyl iodide, obtained in the extraction column 92, can be
recycled to the distillation column 91 through the line 110. The
liquid from the line 113 is usually discharged to the outside as
water discharge. A gas that has not been condensed in the condenser
91a or 93a (line 106 or 116) is subjected to absorption treatment
in the scrubber system 8 or discarded.
[0069] The acetaldehyde derived from the process stream containing
at least the water, the acetic acid (AC), the methyl iodide (MeI),
and the acetaldehyde (AD) can also be separated and removed by use
of extractive distillation, in addition to the method described
above. For example, the organic phase and/or the aqueous phase
(charging mixture) obtained by the separation of the process stream
is fed to a distillation column (extractive distillation column).
In addition, an extraction solvent (usually, water) is introduced
to a concentration zone (e.g., space from the column top to the
charging mixture feeding position) where methyl iodide and
acetaldehyde in the distillation column are concentrated. A liquid
(extract) dropped from the concentration zone is withdrawn as a
side stream (side cut stream). This side stream is separated into
an aqueous phase and an organic phase. The aqueous phase can be
distilled to thereby discharge acetaldehyde to the outside of the
system. In the case where a relatively large amount of water is
present in the distillation column, the liquid dropped from the
concentration zone may be withdrawn as a side stream without
introducing the extraction solvent to the distillation column. For
example, a unit (chimney tray, etc.) that can receive the liquid
(extract) dropped from the concentration zone is disposed in this
distillation column so that a liquid (extract) received by this
unit can be withdrawn as a side stream. The extraction solvent
introduction position is preferably superior to the charging
mixture feeding position, more preferably near the column top. The
side stream withdrawal position is preferably lower than the
extraction solvent introduction position and higher than the
charging mixture feeding position, in the height direction of the
column. According to this method, acetaldehyde can be extracted
with a high concentration from a concentrate of methyl iodide and
the acetaldehyde using an extraction solvent (usually, water). In
addition, the region between the extraction solvent introduction
site and the side cut site is used as an extraction zone.
Therefore, acetaldehyde can be efficiently extracted with a small
amount of the extraction solvent. Therefore, for example, the
number of plates in the distillation column can be drastically
decreased as compared with a method of withdrawing an extract by
extractive distillation from the column bottom of the distillation
column (extractive distillation column). In addition, steam load
can also be reduced. Furthermore, the ratio of methyl iodide to
acetaldehyde (MeI/AD ratio) in a water extract can be decreased as
compared with a method of combining the aldehyde removing
distillation of FIG. 2 with water extraction using a small amount
of an extraction solvent. Therefore, acetaldehyde can be removed
under conditions that can suppress a loss of methyl iodide to the
outside of the system. The acetaldehyde concentration in the side
stream is much higher than the acetaldehyde concentration in the
charging mixture and the bottom fraction (column bottom fraction).
The ratio of acetaldehyde to methyl iodide in the side stream is
larger than the ratio of acetaldehyde to methyl iodide in the
charging mixture and the bottom fraction. The organic phase (methyl
iodide phase) obtained by the separation of the side stream may be
recycled to this distillation column. In this case, the recycle
position of the organic phase obtained by the separation of the
side stream is preferably lower than the side stream withdrawal
position and preferably higher than the charging mixture feeding
position, in the height direction of the column. A solvent miscible
with the components (e.g., methyl acetate) constituting the organic
phase obtained by the separation of the process stream may be
introduced to this distillation column (extractive distillation
column). Examples of the miscible solvent include acetic acid and
ethyl acetate. The miscible solvent introduction position is
preferably lower than the side stream withdrawal position and
preferably higher than the charging mixture feeding position, in
the height direction of the column. Also, the miscible solvent
introduction position is preferably inferior to a recycle position
in the case where the organic phase obtained by the separation of
the side stream is recycled to this distillation column. The
organic phase obtained by the separation of the side stream is
recycled to the distillation column, or the miscible solvent is
introduced to the distillation column, whereby the methyl acetate
concentration in the extract withdrawn as the side stream can be
decreased, and the methyl acetate concentration in the aqueous
phase obtained by the separation of the extract can be lowered.
Hence, the contamination of the aqueous phase with methyl iodide
can be suppressed.
[0070] The theoretical number of plates of the distillation column
(extractive distillation column) is, for example, 1 to 100,
preferably 2 to 50, further preferably 3 to 30, particularly
preferably 5 to 20. Acetaldehyde can be efficiently separated and
removed by a smaller number of plates than 80 to 100 plates in a
distillation column or an extractive distillation column for use in
conventional acetaldehyde removal. The mass ratio between the flow
rate of the extraction solvent and the flow rate of the charging
mixture (the organic phase and/or the aqueous phase obtained by the
separation of the process stream) (former/latter) may be selected
from the range of 0.0001/100 to 100/100 and is usually 0.0001/100
to 20/100, preferably 0.001/100 to 10/100, more preferably 0.01/100
to 8/100, further preferably 0.1/100 to 5/100. The column top
temperature of the distillation column (extractive distillation
column) is, for example, 15 to 120.degree. C., preferably 20 to
90.degree. C., more preferably 20 to 80.degree. C., further
preferably 25 to 70.degree. C. The column top pressure is, on the
order of, for example, 0.1 to 0.5 MPa in terms of absolute
pressure. Other conditions for the distillation column (extractive
distillation column) may be the same as those for a distillation
column or an extractive distillation column for use in conventional
acetaldehyde removal.
[0071] FIG. 3 is a schematic flow diagram showing another example
of the acetaldehyde separation and removal system using the
extractive distillation described above. In this example, the
organic phase and/or the aqueous phase (charging mixture) obtained
by the separation of the process stream is fed to a middle part
(position between the column top and the column bottom) of a
distillation column 94 through a feed line 201, while water is
introduced thereto from near the column top through a line 202 so
that extractive distillation is performed in the distillation
column 94 (extractive distillation column). A chimney tray 200 for
receiving a liquid (extract) dropped from a concentration zone
where methyl iodide and acetaldehyde in the column are concentrated
is disposed superior to the charging mixture feeding position of
the distillation column 94. In this extractive distillation,
preferably the whole amount, of the liquid on the chimney tray 200
is withdrawn, introduced to a decanter 95 through a line 208, and
separated. The aqueous phase (containing acetaldehyde) in the
decanter 95 is introduced to a cooler 95a through a line 212 and
cooled so that methyl iodide dissolved in the aqueous phase is
separated into 2 phases in a decanter 96. The aqueous phase in the
decanter 96 is fed to a distillation column 97 (acetaldehyde
removal column) through a line 216 and distilled. The vapor at the
column top is led to a condenser 97a through a line 217 and
condensed. A portion of the condensate (mainly, acetaldehyde and
methyl iodide) is refluxed to the column top of the distillation
column 97, and the remaining portion is discarded or fed to a
distillation column 98 (extractive distillation column) through a
line 220. Water is introduced thereto from near the column top of
the distillation column 98 through a line 222, followed by
extractive distillation. The vapor at the column top is led to a
condenser 98a through a line 223 and condensed. A portion of the
condensate (mainly, methyl iodide) is refluxed to the column top,
and the remaining portion is recycled to the reaction system
through a line 226, but may be discharged to the outside of the
system. Preferably the whole amount, of the organic phase (methyl
iodide phase) in the decanter 95 is recycled to below the position
of the chimney tray 200 of the distillation column 94 through lines
209 and 210. A portion of the aqueous phase of the decanter 95 and
the organic phase of the decanter 96 are recycled to the
distillation column 94 through lines 213 and 210 and lines 214 and
210, respectively, but may not be recycled. A portion of the
aqueous phase of the decanter 95 may be utilized as an extraction
solvent (water) in the distillation column 94. A portion of the
aqueous phase of the decanter 96 may be recycled to the
distillation column 94 through the line 210. In some cases (e.g.,
the case where methyl acetate is contained in the charging
mixture), a solvent (acetic acid, ethyl acetate, etc.) miscible
with the components (e.g., methyl acetate) constituting the organic
phase obtained by the separation of the process stream may be fed
to the distillation column 94 through a line 215 to thereby improve
distillation efficiency. The feeding position of the miscible
solvent to the distillation column 94 is superior to the charging
mixture feeding portion (junction of the line 201) and inferior to
the junction of the recycle line 210. A bottom fraction of the
distillation column 94 is recycled to the reaction system. A vapor
at the column top of the distillation column 94 is led to a
condenser 94a through a line 203 and condensed. The condensate is
separated in a decanter 99. The organic phase is refluxed to the
column top of the distillation column 94 through a line 206, while
the aqueous phase is led to the decanter 95 through a line 207. A
bottom fraction (water is a main component) of the distillation
column 97 and a bottom fraction (water containing a small amount of
acetaldehyde) of the distillation column 98 (extractive
distillation column) are discharged to the outside of the system
through lines 218 and 224, respectively, or recycled to the
reaction system. A gas that has not been condensed in the condenser
94a, 97a, or 98a (line 211, 221, or 227) is subjected to absorption
treatment in the scrubber system 8, or discarded.
[0072] FIG. 4 is a schematic flow diagram showing a further
alternative example of the acetaldehyde separation and removal
system using the extractive distillation described above. In this
example, a condensate of a vapor from the column top of the
distillation column 94 is led to a hold tank 100, and the whole
amount thereof is refluxed to the column top of the distillation
column 94 through the line 206. The other points are the same as in
the example of FIG. 3.
[0073] FIG. 5 is a schematic flow diagram showing a further
alternative example of the acetaldehyde separation and removal
system using the extractive distillation described above. In this
example, the whole amount of a liquid on the chimney tray 200 is
withdrawn, directly introduced to the cooler 95a through the line
208 without the medium of the decanter 95, cooled, and fed to the
decanter 96. The other points are the same as in the example of
FIG. 4.
[0074] In FIG. 1 described above, the gaseous portion generated in
the condenser 3a contains, for example, carbon monoxide, hydrogen,
methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen
iodide, water, methyl acetate, acetic acid, dimethyl ether,
methanol, acetaldehyde, and formic acid and is fed to the scrubber
system 8 from the condenser 3a through the lines 32 and 15. For
example, methyl iodide, hydrogen iodide, water, methyl acetate,
acetic acid, dimethyl ether, methanol, acetaldehyde, and formic
acid in the gaseous portion that has entered the scrubber system 8
are absorbed to an absorbing liquid in the scrubber system 8. The
hydrogen iodide generates methyl iodide through reaction with
methanol or methyl acetate in the absorbing liquid. Then, a liquid
portion containing useful components such as the methyl iodide is
recycled to the reaction vessel 1 from the scrubber system 8
through the recycle lines 48 and 23 and reused.
[0075] The bottom fraction withdrawn from the column bottom of the
distillation column 3 contains a larger amount of components having
a higher boiling point (higher boiling point components) than that
of acetic acid as compared with the overhead stream and the side
stream from the distillation column 3 and contains, for example,
propionic acid, and the entrained catalyst and co-catalyst
mentioned above. This bottom fraction also contains, for example,
acetic acid, methyl iodide, methyl acetate, and water. In the
present embodiment, a portion of such a bottom fraction is
continuously introduced to the evaporator 2 through the lines 25
and 26 and recycled, and another portion of the bottom fraction is
continuously introduced to the reaction vessel 1 through the lines
25 and 23 and recycled.
[0076] The first acetic acid stream continuously withdrawn as a
side stream from the distillation column 3 is more enriched with
acetic acid than the vapor stream continuously introduced to the
distillation column 3. Specifically, the acetic acid concentration
of the first acetic acid stream is higher than the acetic acid
concentration of the vapor stream. The acetic acid concentration of
the first acetic acid stream is, for example, 90 to 99.9% by mass,
preferably 93 to 99% by mass. Also, the first acetic acid stream
may contain, in addition to acetic acid, for example, methyl
iodide, hydrogen iodide, water, methyl acetate, dimethyl ether,
methanol, acetaldehyde, formic acid, and propionic acid. The
connection position of the line 27 to the distillation column 3 may
be, as shown in the drawing, higher than the connection position of
the line 21 to the distillation column 3 in the height direction of
the distillation column 3, but may be lower than the connection
position of the line 21 to the distillation column 3 or may be the
same as the connection position of the line 21 to the distillation
column 3. The first acetic acid stream from the distillation column
3 is continuously introduced at a predetermined flow rate to the
next distillation column 5 through the line 27. The first acetic
acid stream withdrawn as a side stream from the distillation column
3, column bottom fraction of the distillation column 3, or
condensate of the vapor in the column bottom of the distillation
column 3 may be directly used as product acetic acid, or may be
directly and continuously introduced into the distillation column 6
without using the distillation column 5.
[0077] To the first acetic acid stream flowing through the line 27,
potassium hydroxide can be fed or added through the line 55
(potassium hydroxide introduction line). The potassium hydroxide
can be fed or added, for example, as a solution such as an aqueous
solution. Hydrogen iodide in the first acetic acid stream can be
decreased by the feed or addition of potassium hydroxide to the
first acetic acid stream. Specifically, the hydrogen iodide reacts
with the potassium hydroxide to form potassium iodide and water.
This can reduce the corrosion of an apparatus such as a
distillation column ascribable to hydrogen iodide. In this process,
the potassium hydroxide can be fed or added to an appropriate site
where hydrogen iodide is present. The potassium hydroxide added
during the process also reacts with acetic acid to form potassium
acetate.
[0078] The distillation column 5 is a unit for performing the
second distillation step and serves as the so-called dehydration
column in the present embodiment. The second distillation step is a
step for further purifying acetic acid by the distillation
treatment of the first acetic acid stream continuously introduced
to the distillation column 5. The distillation column 5 consists
of, for example, a distillation column such as a plate column or a
packed column. In the case of adopting a plate column as the
distillation column 5, the theoretical number of plates thereof is,
for example, 5 to 50, and the reflux ratio is, for example, 0.2 to
3000 according to the theoretical number of plates. In the inside
of the distillation column 5 in the second distillation step, the
column top pressure is set to, for example, 150 to 250 kPa (gauge
pressure), and the column bottom pressure is higher than the column
top pressure and is set to, for example, 160 to 290 kPa (gauge
pressure). In the inside of the distillation column 5 in the second
distillation step, the column top temperature is, for example, a
temperature of higher than the boiling point of water and lower
than the boiling point of acetic acid at the set column top
pressure and is set to 130 to 160.degree. C., and the column bottom
temperature is, for example, a temperature of not less than the
boiling point of acetic acid at the set column bottom pressure and
is set to 150 to 175.degree. C.
[0079] A vapor as an overhead stream is continuously withdrawn to
the line 33 from the column top of the distillation column 5. A
bottom fraction is continuously withdrawn to the line 34 from the
column bottom of the distillation column 5. 5b denotes a reboiler.
A side stream (liquid or gas) may be continuously withdrawn to the
line 34 from the height position between the column top and the
column bottom of the distillation column 5.
[0080] The vapor withdrawn from the column top of the distillation
column 5 contains a larger amount of components having a lower
boiling point (lower boiling point components) than that of acetic
acid as compared with the bottom fraction from the distillation
column 5 and contains, for example, methyl iodide, hydrogen iodide,
water, methyl acetate, acetic acid, dimethyl ether, methanol,
acetaldehyde, and formic acid. Such a vapor is continuously
introduced to the condenser 5a through the line 33.
[0081] The condenser 5a separates the vapor from the distillation
column 5 into a condensate portion and a gaseous portion by cooling
and partial condensation. The condensate portion contains, for
example, water and acetic acid. A portion of the condensate portion
is continuously refluxed to the distillation column 5 from the
condenser 5a through the line 35. Another portion of the condensate
portion is continuously introduced to the reaction vessel 1 from
the condenser 5a through the lines 35, 36, and 23 and recycled. The
gaseous portion generated in the condenser 5a contains, for
example, carbon monoxide, hydrogen, methane, carbon dioxide,
nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl
acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and
formic acid and is fed to the scrubber system 8 from the condenser
5a through the lines 37 and 15. Hydrogen iodide in the gaseous
portion that has entered the scrubber system 8 is absorbed to an
absorbing liquid in the scrubber system 8. Methyl iodide is
generated through the reaction of the hydrogen iodide with methanol
or methyl acetate in the absorbing liquid. Then, a liquid portion
containing useful components such as the methyl iodide is recycled
to the reaction vessel 1 from the scrubber system 8 through the
recycle lines 48 and 23 and reused.
[0082] The bottom fraction (or the side stream) withdrawn from the
column bottom of the distillation column 5 contains a larger amount
of components having a higher boiling point (higher boiling point
components) than that of acetic acid as compared with the overhead
stream from the distillation column 5 and contains, for example,
propionic acid, potassium acetate (in the case of feeding potassium
hydroxide to the line 27, etc.), and the entrained catalyst and
co-catalyst mentioned above. This bottom fraction may also contain
acetic acid. Such a bottom fraction is continuously introduced in
the form of the second acetic acid stream to the next distillation
column 6 through the line 34.
[0083] In the present invention, it is preferred that the
distillation step using the distillation column (dehydration
column) 5 should satisfy the operating conditions (ii) involving a
hydrogen partial pressure of not more than 5 kPa (absolute
pressure), a carbon dioxide partial pressure of less than 20 kPa
(absolute pressure), and an operating temperature of more than
100.degree. C. In this case, the hydrogen partial pressure
(absolute pressure) is preferably not more than 2 kPa, more
preferably not more than 1 kPa, further preferably not more than
0.5 kPa. The lower limit of the hydrogen partial pressure (absolute
pressure) is 0 kPa. The carbon dioxide partial pressure (absolute
pressure) is preferably not more than 5 kPa, more preferably not
more than 2 kPa, further preferably not more than 1 kPa (e.g., not
more than 0.5 kPa). The lower limit of the carbon dioxide partial
pressure (absolute pressure) is 0 kPa. The operating temperature is
preferably not less than 120.degree. C., more preferably not less
than 130.degree. C. The upper limit of the operating temperature
is, for example, 170.degree. C., preferably 165.degree. C., more
preferably 160.degree. C., further preferably 155.degree. C.
[0084] In the case where the distillation step using the
distillation column (dehydration column) 5 satisfies the operating
conditions (ii), the charging mixture for the distillation column 5
may have an acetic acid concentration of not less than 30% by mass
(e.g., 30 to 99.999% by mass) and a formic acid concentration of
not less than 5 ppm by mass (e.g., 5 to 10000 ppm by mass). Also,
the charging mixture for the distillation column 5 has an acetic
acid concentration of preferably 80 to 99.9% by mass (e.g., 90 to
99.9% by mass, particularly, 93 to 99% by mass), a methyl iodide
concentration of preferably 0.01 to 16% by mass (e.g., 0.1 to 8% by
mass, particularly, 0.2 to 5% by mass), a water concentration of
preferably 0.05 to 18% by mass (e.g., 0.1 to 8% by mass,
particularly, 0.2 to 5% by mass), a methyl acetate concentration of
preferably 0.01 to 16% by mass (e.g., 0.1 to 8% by mass,
particularly, 0.2 to 5% by mass), and a formic acid concentration
of preferably 5 to 10000 ppm by mass (e.g., 10 to 1000 ppm by mass,
more preferably 10 to 500 ppm by mass, particularly, 15 to 200 ppm
by mass, in particular, 20 to 100 ppm by mass). The distillation
step using the distillation column 5 satisfies the operating
conditions (ii), whereby formic acid formation in the distillation
column 5 is suppressed. In addition, when a liquid containing
formic acid is fed to the distillation column 5, the formic acid is
efficiently decomposed.
[0085] The second acetic acid stream is more enriched with acetic
acid than the first acetic acid stream continuously introduced to
the distillation column 5. Specifically, the acetic acid
concentration of the second acetic acid stream is higher than the
acetic acid concentration of the first acetic acid stream. The
acetic acid concentration of the second acetic acid stream is, for
example, 99.1 to 99.99% by mass as long as being higher than the
acetic acid concentration of the first acetic acid stream. Also,
the second acetic acid stream may contain, as described above, in
addition to acetic acid, for example, propionic acid and hydrogen
iodide. In the present embodiment, in the case of withdrawing a
side stream, the withdrawal position of the side stream from the
distillation column 5 is lower than the introduction position of
the first acetic acid stream to the distillation column 5 in the
height direction of the distillation column 5.
[0086] To the second acetic acid stream flowing through the line
34, potassium hydroxide can be fed or added through the line 56
(potassium hydroxide introduction line). The potassium hydroxide
can be fed or added, for example, as a solution such as an aqueous
solution. Hydrogen iodide in the second acetic acid stream can be
decreased by the feed or addition of potassium hydroxide to the
second acetic acid stream. Specifically, the hydrogen iodide reacts
with the potassium hydroxide to form potassium iodide and water.
This can reduce the corrosion of an apparatus such as a
distillation column ascribable to hydrogen iodide.
[0087] The distillation column 6 is a unit for performing the third
distillation step and serves as the so-called higher boiling point
component removal column in the present embodiment. The third
distillation step is a step for further purifying acetic acid by
the purification treatment of the second acetic acid stream
continuously introduced to the distillation column 6. The
distillation column 6 consists of, for example, a distillation
column such as a plate column or a packed column. In the case of
adopting a plate column as the distillation column 6, the
theoretical number of plates thereof is, for example, 5 to 50, and
the reflux ratio is, for example, 0.2 to 3000 according to the
theoretical number of plates. In the inside of the distillation
column 6 in the third distillation step, the column top pressure is
set to, for example, -100 to 150 kPa (gauge pressure), and the
column bottom pressure is higher than the column top pressure and
is set to, for example, -90 to 180 kPa (gauge pressure). In the
inside of the distillation column 6 in the third distillation step,
the column top temperature is, for example, a temperature of higher
than the boiling point of water and lower than the boiling point of
acetic acid at the set column top pressure and is set to 50 to
150.degree. C., and the column bottom temperature is, for example,
a temperature of higher than the boiling point of acetic acid at
the set column bottom pressure and is set to 70 to 160.degree.
C.
[0088] A vapor as an overhead stream is continuously withdrawn to
the line 38 from the column top of the distillation column 6. A
bottom fraction is continuously withdrawn to the line 39 from the
column bottom of the distillation column 6. 6b denotes a reboiler.
A side stream (liquid or gas) is continuously withdrawn to the line
46 from the height position between the column top and the column
bottom of the distillation column 6. The connection position of the
line 46 to the distillation column 6 may be, as shown in the
drawing, higher than the connection position of the line 34 to the
distillation column 6 in the height direction of the distillation
column 6, but may be lower than the connection position of the line
34 to the distillation column 6 or may be the same as the
connection position of the line 34 to the distillation column
6.
[0089] The vapor withdrawn from the column top of the distillation
column 6 contains a larger amount of components having a lower
boiling point (lower boiling point components) than that of acetic
acid as compared with the bottom fraction from the distillation
column 6 and contains, in addition to acetic acid, for example,
methyl iodide, hydrogen iodide, water, methyl acetate, dimethyl
ether, methanol, and formic acid. Such a vapor is continuously
introduced to the condenser 6a through the line 38.
[0090] The condenser 6a separates the vapor from the distillation
column 6 into a condensate portion and a gaseous portion by cooling
and partial condensation. The condensate portion contains, in
addition to acetic acid, for example, methyl iodide, hydrogen
iodide, water, methyl acetate, dimethyl ether, methanol, and formic
acid. At least a portion of the condensate portion is continuously
refluxed to the distillation column 6 from the condenser 6a through
the line 40. A portion (distillate) of the condensate portion may
be recycled to the first acetic acid stream in the line 27 before
introduction to the distillation column 5 from the condenser 6a
through the lines 40, 41, and 42. Together with this or instead of
this, a portion (distillate) of the condensate portion may be
recycled to the vapor stream in the line 21 before introduction to
the distillation column 3 from the condenser 6a through the lines
40, 41, and 43. Also, a portion (distillate) of the condensate
portion may be recycled to the reaction vessel 1 from the condenser
6a through the lines 40, 44, and 23. Furthermore, as mentioned
above, a portion of the distillate from the condenser 6a may be fed
to the scrubber system 8 and used as an absorbing liquid in this
system. In the scrubber system 8, a gaseous portion after
absorption of a useful portion is discharged to the outside of the
apparatus. Then, a liquid portion containing the useful components
is introduced or recycled to the reaction vessel 1 from the
scrubber system 8 through the recycle lines 48 and 23 and reused.
In addition, a portion of the distillate from the condenser 6a may
be led to various pumps (not shown) operated in the apparatus,
through lines (not shown) and used as sealing solutions in these
pumps. In addition, a portion of the distillate from the condenser
6a may be steadily withdrawn to the outside of the apparatus
through a withdrawal line attached to the line 40, or may be
non-steadily withdrawn to the outside of the apparatus when needed.
In the case where a portion (distillate) of the condensate portion
is removed from the distillation treatment system in the
distillation column 6, the amount of the distillate (ratio of the
distillate) is, for example, 0.01 to 30% by mass, preferably 0.1 to
10% by mass, more preferably 0.3 to 5% by mass, more preferably 0.5
to 3% by mass, of the condensate generated in the condenser 6a. On
the other hand, the gaseous portion generated in the condenser 6a
contains, for example, carbon monoxide, hydrogen, methane, carbon
dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water,
methyl acetate, acetic acid, dimethyl ether, methanol,
acetaldehyde, and formic acid and is fed to the scrubber system 8
from the condenser 6a through the lines 45 and 15.
[0091] The bottom fraction withdrawn from the column bottom of the
distillation column 6 through the line 39 contains a larger amount
of components having a higher boiling point (higher boiling point
components) than that of acetic acid as compared with the overhead
stream from the distillation column 6 and contains, for example,
propionic acid and potassium acetate (in the case of feeding
potassium hydroxide to the line 34, etc.). Also, the bottom
fraction withdrawn from the column bottom of the distillation
column 6 through the line 39 also contains, for example, a corroded
metal such as a metal formed at and released from the inside wall
of a member constituting this acetic acid production apparatus, and
a compound of iodine derived from corrosive iodine and the corroded
metal, etc. In the present embodiment, such a bottom fraction is
discharged to the outside of the acetic acid production
apparatus.
[0092] The side stream continuously withdrawn to the line 46 from
the distillation column 6 is continuously introduced as a third
acetic acid stream to the next ion exchange resin column 7. This
third acetic acid stream is more enriched with acetic acid than the
second acetic acid stream continuously introduced to the
distillation column 6. Specifically, the acetic acid concentration
of the third acetic acid stream is higher than the acetic acid
concentration of the second acetic acid stream. The acetic acid
concentration of the third acetic acid stream is, for example, 99.8
to 99.999% by mass as long as being higher than the acetic acid
concentration of the second acetic acid stream. In the present
embodiment, the withdrawal position of the side stream from the
distillation column 6 is higher than the introduction position of
the second acetic acid stream to the distillation column 6 in the
height direction of the distillation column 6. In another
embodiment, the withdrawal position of the side stream from the
distillation column 6 is the same as or lower than the introduction
position of the second acetic acid stream to the distillation
column 6 in the height direction of the distillation column 6. A
simple distillator (evaporator) may be used in place of the
distillation column 6. Also, the distillation column 6 can be
omitted as long as the removal of impurities in the distillation
column 5 is adequately performed.
[0093] In the present invention, it is preferred that the
distillation step using the distillation column (higher boiling
point component removal column) 6 should satisfy the operating
conditions (ii) involving a hydrogen partial pressure of not more
than 5 kPa (absolute pressure), a carbon dioxide partial pressure
of less than 20 kPa (absolute pressure), and an operating
temperature of more than 100.degree. C. In this case, the hydrogen
partial pressure (absolute pressure) is preferably not more than 2
kPa, more preferably not more than 1 kPa, further preferably not
more than 0.5 kPa. The lower limit of the hydrogen partial pressure
(absolute pressure) is 0 kPa. The carbon dioxide partial pressure
(absolute pressure) is preferably not more than 5 kPa, more
preferably not more than 2 kPa, further preferably not more than 1
kPa (e.g., not more than 0.5 kPa). The lower limit of the carbon
dioxide partial pressure (absolute pressure) is 0 kPa. The
operating temperature is preferably not less than 120.degree. C.,
more preferably not less than 130.degree. C. The upper limit of the
operating temperature is, for example, 165.degree. C., preferably
160.degree. C., further preferably 155.degree. C.
[0094] In the case where the distillation step using the
distillation column (higher boiling point component removal column)
6 satisfies the operating conditions (ii), the charging mixture for
the distillation column 6 has an acetic acid concentration of
preferably 99.1 to 99.99% by mass and a formic acid concentration
of preferably 5 to 9000 ppm by mass (e.g., 10 to 1000 ppm by mass,
more preferably 10 to 500 ppm by mass, particularly, 15 to 200 ppm
by mass, in particular, 20 to 100 ppm by mass). The distillation
step using the distillation column 6 satisfies the operating
conditions (ii), whereby formic acid formation in the distillation
column 6 is suppressed. In addition, when a liquid containing
formic acid is fed to the distillation column 6, the formic acid is
efficiently decomposed.
[0095] The ion exchange resin column 7 is a purification unit for
performing the adsorptive removal step. This adsorptive removal
step is a step for further purifying acetic acid by the adsorptive
removal of, mainly, alkyl iodides (hexyl iodide, decyl iodide,
etc.) contained in a very small amount in the third acetic acid
stream continuously introduced to the ion exchange resin column 7.
In the ion exchange resin column 7, an ion exchange resin having
the ability to adsorb alkyl iodides is packed in the column to
establish an ion exchange resin bed. Examples of such an ion
exchange resin can include cation exchange resins in which a
portion of leaving protons in an exchange group such as a sulfonic
acid group, a carboxyl group, or a phosphonic acid group is
substituted by a metal such as silver or copper. In the adsorptive
removal step, for example, the third acetic acid stream (liquid)
flows through the inside of the ion exchange resin column 7 packed
with such an ion exchange resin, and in the course of this flow,
impurities such as the alkyl iodides in the third acetic acid
stream are adsorbed to the ion exchange resin and removed from the
third acetic acid stream. In the ion exchange resin column 7 in the
adsorptive removal step, the internal temperature is, for example,
18 to 100.degree. C., and the rate of the acetic acid stream [the
throughput of acetic acid per m.sup.3 resin volume (m.sup.3/h)] is,
for example, 3 to 15 m.sup.3/hm.sup.3 (resin volume).
[0096] A fourth acetic acid stream is continuously led to the line
47 from the lower end of the ion exchange resin column 7. The
acetic acid concentration of the fourth acetic acid stream is
higher than the acetic acid concentration of the third acetic acid
stream. Specifically, the fourth acetic acid stream is more
enriched with acetic acid than the third acetic acid stream
continuously introduced to the ion exchange resin column 7. The
acetic acid concentration of the fourth acetic acid stream is, for
example, 99.9 to 99.999% by mass or not less than this range as
long as being higher than the acetic acid concentration of the
third acetic acid stream. In this production method, this fourth
acetic acid stream can be retained in a product tank (not
shown).
[0097] In this acetic acid production apparatus, a so-called
product column or finishing column which is a distillation column
may be disposed as a purification unit for further purifying the
fourth acetic acid stream from the ion exchange resin column 7. In
the case where such a product column is disposed, the product
column consists of, for example, a distillation column such as a
plate column or a packed column. In the case of adopting a plate
column as the product column, the theoretical number of plates
thereof is, for example, 5 to 50, and the reflux ratio is, for
example, 0.5 to 3000 according to the theoretical number of plates.
In the inside of the product column in the purification step, the
column top pressure is set to, for example, -195 to 150 kPa (gauge
pressure), and the column bottom pressure is higher than the column
top pressure and is set to, for example, -190 to 180 kPa (gauge
pressure). In the inside of the product column, the column top
temperature is, for example, a temperature of higher than the
boiling point of water and lower than the boiling point of acetic
acid at the set column top pressure and is set to 50 to 150.degree.
C., and the column bottom temperature is, for example, a
temperature of higher than the boiling point of acetic acid at the
set column bottom pressure and is set to 70 to 160.degree. C. A
simple distillator (evaporator) may be used in place of the product
column or the finishing column.
[0098] In the case of disposing the product column, the whole or a
portion of the fourth acetic acid stream (liquid) from the ion
exchange resin column 7 is continuously introduced to the product
column. A vapor as an overhead stream containing a very small
amount of lower boiling point components (e.g., methyl iodide,
water, methyl acetate, dimethyl ether, crotonaldehyde,
acetaldehyde, and formic acid) is continuously withdrawn from the
column top of such a product column. This vapor is separated into a
condensate portion and a gaseous portion in a predetermined
condenser. A portion of the condensate portion is continuously
refluxed to the product column, and another portion of the
condensate portion may be recycled to the reaction vessel 1 or
discarded to the outside of the system, or both. The gaseous
portion is fed to the scrubber system 8. A bottom fraction
containing a very small amount of higher boiling point components
is continuously withdrawn from the column bottom of the product
column. This bottom fraction is recycled to, for example, the
second acetic acid stream in the line 34 before introduction to the
distillation column 6. A side stream (liquid) is continuously
withdrawn as a fifth acetic acid stream from the height position
between the column top and the column bottom of the product column.
The withdrawal position of the side stream from the product column
is lower than, for example, the introduction position of the fourth
acetic acid stream to the product column in the height direction of
the product column. The fifth acetic acid stream is more enriched
with acetic acid than the fourth acetic acid stream continuously
introduced to the product column. Specifically, the acetic acid
concentration of the fifth acetic acid stream is higher than the
acetic acid concentration of the fourth acetic acid stream. The
acetic acid concentration of the fifth acetic acid stream is, for
example, 99.9 to 99.999% by mass or not less than this range as
long as being higher than the acetic acid concentration of the
fourth acetic acid stream. This fifth acetic acid stream is
retained in, for example, a product tank (not shown). The ion
exchange resin column 7 may be placed downstream of the product
column instead of (or in addition to) its placement downstream of
the distillation column 6 to treat the acetic acid stream from the
product column.
[0099] In the present invention, it is preferred that the
distillation step using the distillation column (product column)
should satisfy the operating conditions (ii) involving a hydrogen
partial pressure of not more than 5 kPa (absolute pressure), a
carbon dioxide partial pressure of less than 20 kPa (absolute
pressure), and an operating temperature of more than 100.degree. C.
In this case, the hydrogen partial pressure (absolute pressure) is
preferably not more than 2 kPa, more preferably not more than 1
kPa, further preferably not more than 0.5 kPa. The lower limit of
the hydrogen partial pressure (absolute pressure) is 0 kPa. The
carbon dioxide partial pressure (absolute pressure) is preferably
not more than 5 kPa, more preferably not more than 2 kPa, further
preferably not more than 1 kPa (e.g., not more than 0.5 kPa). The
lower limit of the carbon dioxide partial pressure (absolute
pressure) is 0 kPa. The operating temperature is preferably not
less than 120.degree. C., more preferably not less than 130.degree.
C. The upper limit of the operating temperature is, for example,
165.degree. C., preferably 160.degree. C., more preferably
155.degree. C.
[0100] In the case where the distillation step using the
distillation column (product column) satisfies the operating
conditions (ii), the charging mixture for the distillation column
(product column) has an acetic acid concentration of preferably
99.8 to 99.999% by mass and a formic acid concentration of
preferably 5 to 2000 ppm by mass (e.g., 5 to 1000 ppm by mass,
particularly, 5 to 100 ppm by mass). The distillation step using
the distillation column (product column) satisfies the operating
conditions (ii), whereby formic acid formation in the distillation
column (product column) is suppressed. In addition, when a liquid
containing formic acid is fed to the distillation column (product
column), the formic acid is efficiently decomposed.
[0101] In the embodiments described above, it is preferred that, as
mentioned above, the retention time in the step that satisfies the
operating conditions (i) or the step that satisfies the operating
conditions (ii) should be not less than 1 minute (e.g., not less
than 5 minutes, particularly, not less than 10 minutes). The upper
limit of the retention time is, for example, 2 hours, preferably 1
hour.
[0102] Also, a process solution having a formic acid concentration
of not less than 10 ppm by mass (e.g., 10 to 10000 ppm by mass,
preferably 15 to 1000 ppm by mass, further preferably 20 to 200 ppm
by mass) may be recycled to a step that satisfies (iii) operating
conditions involving a hydrogen partial pressure of less than 500
kPa (absolute pressure), a carbon dioxide partial pressure of less
than 70 kPa (absolute pressure), and an operating temperature of
more than 100.degree. C. Examples of the step that satisfies the
operating conditions (iii) include the reaction step, the
evaporation step, and the distillation steps (e.g., the lower
boiling point component removal step and the dehydration step). The
step that satisfies the operating conditions (iii) includes the
step that satisfies the operating conditions (i) and the step that
satisfies the operating conditions (ii). The process solution
having a formic acid concentration of not less than 10 ppm by mass)
is recycled to the step that satisfies the operating conditions
(iii) so that the formic acid contained in the process solution is
efficiently decomposed in this step.
[0103] Furthermore, a column top fraction of the distillation
column in at least one distillation step, for example, the lower
boiling point component removal step, the dehydration step, the
higher boiling point component removal step, or the product step
may be recycled to the step that satisfies the operating conditions
(i) or the step that satisfies the operating conditions (ii).
Examples of the step that satisfies the operating conditions (i)
and the step that satisfies the operating conditions (ii) include
the reaction step, the evaporation step, the lower boiling point
component removal step, and the dehydration step. In this case, it
is preferred that the step to which the column top fraction of the
distillation column is recycled should be the reaction step or
should be the evaporation step or a distillation step (e.g., the
lower boiling point component removal step, the dehydration step,
or the higher boiling point component removal step) positioned
upstream from the distillation step associated with the
distillation column.
EXAMPLES
[0104] Hereinafter, the present invention will be described in more
detail with reference to Examples. However, the present invention
is not intended to be limited by these Examples. "MeI" represents
methyl iodide, and "MA" represents methyl acetate. In the
compositional analysis of a liquid phase portion, a water
concentration was measured by the Karl Fischer water determination
method; a formic acid concentration was measured by liquid
chromatography; a rhodium concentration was measured by ICP
analysis (or atomic adsorption analysis); as for a lithium iodide
concentration, Li was measured by ICP analysis, and iodine was
measured by electrometric titration analysis; and concentrations of
other components were measured by gas chromatography. The partial
pressure of each gaseous component in a gaseous phase portion was
calculated from total pressure and each gaseous component
concentration measured by gas chromatography. The units "%" and
"ppm" mean "% by mass" and "ppm by mass", respectively.
Comparative Example 1
[0105] 10% of MeI, 4% of MA, 2.5% of water, 15% of LiI, 500 ppm (in
terms of the metal) of a rhodium complex catalyst
([Rh(CO).sub.2I.sub.2].sup.-), and acetic acid as a balance were
fed as raw materials in initial introduction composition to a 1000
ml zirconium autoclave. After purging with N.sub.2 (holding at
N.sub.2 atmospheric pressure), H.sub.2, CO.sub.2, and CO were fed
to the autoclave to make a H.sub.2 partial pressure of 510 kPa
(absolute pressure), a CO.sub.2 partial pressure of 70 kPa
(absolute pressure), and a CO partial pressure of 1.6 MPa (absolute
pressure). The autoclave was held for 30 minutes with the
temperature kept at 180.degree. C. in an oil bath. After cooling,
the liquid was sampled and subjected to compositional analysis. As
a result, the formic acid concentration was 88 ppm. Although the MA
concentration was decreased to 0.1%, there was no large change in
the composition of the other components. Results of compositional
analysis at the start of the experiment, after 8 minutes into the
experiment, and at the completion of the experiment, and the formic
acid concentration at the completion of the experiment are shown in
the table below.
Comparative Example 2
[0106] The same experiment as in Comparative Example 1 was
conducted except that: 10% of MeI, 5% of MA, 2.5% of water, 15% of
LiI, 500 ppm (in terms of the metal) of a rhodium complex catalyst
([Rh(CO).sub.2I.sub.2].sup.-), and acetic acid as a balance were
fed as the initial introduction composition; H.sub.2, CO.sub.2, and
CO were fed to the autoclave to make a H.sub.2 partial pressure of
510 kPa (absolute pressure), a CO.sub.2 partial pressure of 70 kPa
(absolute pressure), and a CO partial pressure of 1.5 MPa (absolute
pressure); and the autoclave was held at a temperature of
170.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 102 ppm. Although the MA
concentration was decreased to 0.1%, there was no large change in
the composition of the other components. Results of compositional
analysis at the start of the experiment and after 9 minutes into
the experiment, and the formic acid concentration at the completion
of the experiment are shown in the table below.
Comparative Example 3
[0107] The same experiment as in Comparative Example 1 was
conducted except that: 40% of MeI, 5% of MA, 2% of water, 52 ppm of
formic acid, and acetic acid as a balance were fed as the initial
introduction composition; H.sub.2, CO.sub.2, and CO were fed to the
autoclave to make a H.sub.2 partial pressure of 5 kPa (absolute
pressure), a CO.sub.2 partial pressure of 10 kPa (absolute
pressure), and a CO partial pressure of 20 kPa (absolute pressure);
and the autoclave was held at a temperature of 100.degree. C. for
30 minutes. After cooling, the liquid was sampled and subjected to
compositional analysis. As a result, the formic acid concentration
was 49 ppm. Since no catalyst was added, carbonylation reaction did
not occur so that there was no change in the basic composition
except for formic acid. Results of compositional analysis at the
start of the experiment and at the completion of the experiment,
and the formic acid concentration at the completion of the
experiment are shown in the table below.
Comparative Example 4
[0108] The same experiment as in Comparative Example 1 was
conducted except that: 50% of water, 5% of MeI, 5% of MA, 50 ppm of
formic acid, and acetic acid as a balance were fed as the initial
introduction composition; H.sub.2, CO.sub.2, and CO were fed to the
autoclave to make a H.sub.2 partial pressure of 5 kPa (absolute
pressure), a CO.sub.2 partial pressure of 2 kPa (absolute
pressure), and a CO partial pressure of 10 kPa (absolute pressure);
and the autoclave was held at a temperature of 100.degree. C. for
30 minutes. After cooling, the liquid was sampled and subjected to
compositional analysis. As a result, the formic acid concentration
was 48 ppm. Since no catalyst was added, carbonylation reaction did
not occur so that there was no change in the basic composition
except for formic acid. Results of compositional analysis at the
start of the experiment, and the formic acid concentration at the
completion of the experiment are shown in the table below.
Comparative Example 5
[0109] The same experiment as in Comparative Example 1 was
conducted except that: 0.2% of water, 51 ppm of formic acid, and
acetic acid as a balance were fed as the initial introduction
composition; H.sub.2, CO.sub.2, and CO were fed to the autoclave to
make a H.sub.2 partial pressure of 1 kPa (absolute pressure), a
CO.sub.2 partial pressure of 1 kPa (absolute pressure), and a CO
partial pressure of 10 kPa (absolute pressure); and the autoclave
was held at a temperature of 100.degree. C. for 30 minutes. After
cooling, the liquid was sampled and subjected to compositional
analysis. As a result, the formic acid concentration was 50 ppm.
Since no catalyst was added, carbonylation reaction did not occur
so that there was no change in the basic composition except for
formic acid. Results of compositional analysis at the start of the
experiment, and the formic acid concentration at the completion of
the experiment are shown in the table below.
Comparative Example 6
[0110] The same experiment as in Comparative Example 1 was
conducted except that: 1.0% of MeI, 1.1% of MA, 2.3% of water,
19.5% of LiI, 670 ppm (in terms of the metal) of a rhodium complex
catalyst ([Rh(CO).sub.2I.sub.2].sup.-), 50 ppm of formic acid, and
acetic acid as a balance were fed as the initial introduction
composition; H.sub.2, CO.sub.2, and CO were fed to the autoclave to
make a H.sub.2 partial pressure of 5.3 kPa (absolute pressure), a
CO.sub.2 partial pressure of 23 kPa (absolute pressure), and a CO
partial pressure of 0.004 MPa (absolute pressure); and the
autoclave was held at a temperature of 145.degree. C. for 5
minutes. After cooling, the liquid was sampled and subjected to
compositional analysis. As a result, the formic acid concentration
was 49 ppm. The MA concentration was 1.0% and was thus hardly
changed. There was no large change in the composition of the other
components. Results of compositional analysis at the start of the
experiment, and the formic acid concentration at the completion of
the experiment are shown in the table below.
Example 1
[0111] The same experiment as in Comparative Example 1 was
conducted except that: 10% of MeI, 4% of MA, 2.5% of water, 15% of
LiI, 500 ppm (in terms of the metal) of a rhodium complex catalyst
([Rh(CO).sub.2I.sub.2].sup.-), and acetic acid as a balance were
fed as the initial introduction composition; and H.sub.2, CO.sub.2,
and CO were fed to the autoclave to make a H.sub.2 partial pressure
of 105 kPa (absolute pressure), a CO.sub.2 partial pressure of 69
kPa (absolute pressure), and a CO partial pressure of 1.6 MPa
(absolute pressure). After cooling, the liquid was sampled and
subjected to compositional analysis. As a result, the formic acid
concentration was 48 ppm. Although the MA concentration was
decreased to 0.1%, there was no large change in the composition of
the other components. Results of compositional analysis at the
start of the experiment and after 8 minutes into the experiment,
and the formic acid concentration at the completion of the
experiment are shown in the table below.
Example 2
[0112] The same experiment as in Example 1 was conducted except
that: 10% of MeI, 4% of MA, 2% of water, 15% of LiI, 500 ppm (in
terms of the metal) of a rhodium complex catalyst
([Rh(CO).sub.2I.sub.2].sup.-), and acetic acid as a balance were
fed as the initial introduction composition; and H.sub.2, CO.sub.2,
and CO were fed to the autoclave to make a H.sub.2 partial pressure
of 50 kPa (absolute pressure), a CO.sub.2 partial pressure of 65
kPa (absolute pressure), and a CO partial pressure of 1.6 MPa
(absolute pressure). After cooling, the liquid was sampled and
subjected to compositional analysis. As a result, the formic acid
concentration was 35 ppm. Although the MA concentration was
decreased to 0.1%, there was no large change in the composition of
the other components. Results of compositional analysis at the
start of the experiment and after 6 minutes into the experiment,
and the formic acid concentration at the completion of the
experiment are shown in the table below.
Example 3
[0113] The same experiment as in Example 1 was conducted except
that: 10% of MeI, 4% of MA, 2% of water, 15% of LiI, 500 ppm (in
terms of the metal) of a rhodium complex catalyst
([Rh(CO).sub.2I.sub.2].sup.-), and acetic acid as a balance were
fed as the initial introduction composition; and H.sub.2, CO.sub.2,
and CO were fed to the autoclave to make a H.sub.2 partial pressure
of 20 kPa (absolute pressure), a CO.sub.2 partial pressure of 60
kPa (absolute pressure), and a CO partial pressure of 1.6 MPa
(absolute pressure). After cooling, the liquid was sampled and
subjected to compositional analysis. As a result, the formic acid
concentration was 28 ppm. Although the MA concentration was
decreased to 0.1%, there was no large change in the composition of
the other components. Results of compositional analysis at the
start of the experiment and after 5 minutes into the experiment,
and the formic acid concentration at the completion of the
experiment are shown in the table below.
Example 4
[0114] The same experiment as in Comparative Example 1 was
conducted except that the autoclave was held at a temperature of
188.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 21 ppm. Although the MA concentration
was decreased to 0.1%, there was no large change in the composition
of the other components. Results of compositional analysis at the
start of the experiment and after 8 minutes into the experiment,
and the formic acid concentration at the completion of the
experiment are shown in the table below.
Example 5
[0115] The same experiment as in Comparative Example 3 was
conducted except that the autoclave was held at a temperature of
110.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 45 ppm. Since no catalyst was added,
carbonylation reaction did not occur so that there was no change in
the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 6
[0116] The same experiment as in Comparative Example 4 was
conducted except that the autoclave was held at a temperature of
110.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 43 ppm. Since no catalyst was added,
carbonylation reaction did not occur so that there was no change in
the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 7
[0117] The same experiment as in Comparative Example 5 was
conducted except that the autoclave was held at a temperature of
110.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 44 ppm. Since no catalyst was added,
carbonylation reaction did not occur so that there was no change in
the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 8
[0118] The same experiment as in Comparative Example 3 was
conducted except that the autoclave was held at a temperature of
120.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 38 ppm. Since no catalyst was added,
carbonylation reaction did not occur so that there was no change in
the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 9
[0119] The same experiment as in Comparative Example 4 was
conducted except that the autoclave was held at a temperature of
120.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 32 ppm. Since no catalyst was added,
carbonylation reaction did not occur so that there was no change in
the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 10
[0120] The same experiment as in Comparative Example 5 was
conducted except that the autoclave was held at a temperature of
120.degree. C. for 30 minutes. After cooling, the liquid was
sampled and subjected to compositional analysis. As a result, the
formic acid concentration was 36 ppm. Since no catalyst was added,
carbonylation reaction did not occur so that there was no change in
the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 11
[0121] The same experiment as in Comparative Example 5 was
conducted except that: in the initial introduction composition, the
water concentration was changed to 0.1%, and the formic acid
concentration was changed to 52 ppm; and the autoclave was held at
a temperature of 140.degree. C. for 30 minutes. After cooling, the
liquid was sampled and subjected to compositional analysis. As a
result, the formic acid concentration was 22 ppm. Since no catalyst
was added, carbonylation reaction did not occur so that there was
no change in the basic composition except for formic acid. Results
of compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 12
[0122] The same experiment as in Comparative Example 5 was
conducted except that: in the initial introduction composition, the
water concentration was changed to 0.1%, and the formic acid
concentration was changed to 52 ppm; and the autoclave was held at
a temperature of 150.degree. C. for 30 minutes. After cooling, the
liquid was sampled and subjected to compositional analysis. As a
result, the formic acid concentration was 13 ppm. Since no catalyst
was added, carbonylation reaction did not occur so that there was
no change in the basic composition except for formic acid. Results
of compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 13
[0123] The same experiment as in Comparative Example 5 was
conducted except that: in the initial introduction composition, the
water concentration was changed to 0.1%, and the formic acid
concentration was changed to 52 ppm; no CO was fed; and the
autoclave was held at a temperature of 150.degree. C. for 30
minutes. After cooling, the liquid was sampled and subjected to
compositional analysis. As a result, the formic acid concentration
was 15 ppm. Since no catalyst was added, carbonylation reaction did
not occur so that there was no change in the basic composition
except for formic acid. Results of compositional analysis at the
start of the experiment, and the formic acid concentration at the
completion of the experiment are shown in the table below.
Example 14
[0124] The same experiment as in Comparative Example 4 was
conducted except that: the initial introduction composition was
changed to 5% of MeI, 5% of MA, 5% of water, 50 ppm of formic acid,
and acetic acid as a balance; and the autoclave was held at a
temperature of 150.degree. C. for 30 minutes. After cooling, the
liquid was sampled and subjected to compositional analysis. As a
result, the formic acid concentration was 17 ppm. Since no catalyst
was added, carbonylation reaction did not occur so that there was
no change in the basic composition except for formic acid. Results
of compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 15
[0125] The same experiment as in Example 8 was conducted except
that H.sub.2, CO.sub.2, and CO were fed to the autoclave to make a
H.sub.2 partial pressure of 0.5 kPa (absolute pressure), a CO.sub.2
partial pressure of 0.3 kPa (absolute pressure), and a CO partial
pressure of 4 kPa (absolute pressure). After cooling, the liquid
was sampled and subjected to compositional analysis. As a result,
the formic acid concentration was 31 ppm. Since no catalyst was
added, carbonylation reaction did not occur so that there was no
change in the basic composition except for formic acid. Results of
compositional analysis at the start of the experiment, and the
formic acid concentration at the completion of the experiment are
shown in the table below.
Example 16
[0126] The same experiment as in Example 15 was conducted except
that the retention time was changed to 5 minutes. After cooling,
the liquid was sampled and subjected to compositional analysis. As
a result, the formic acid concentration was 39 ppm. Since no
catalyst was added, carbonylation reaction did not occur so that
there was no change in the basic composition except for formic
acid. Results of compositional analysis at the start of the
experiment, and the formic acid concentration at the completion of
the experiment are shown in the table below.
Example 17
[0127] The same experiment as in Example 15 was conducted except
that the retention time was changed to 2 minutes. After cooling,
the liquid was sampled and subjected to compositional analysis. As
a result, the formic acid concentration was 44 ppm. Since no
catalyst was added, carbonylation reaction did not occur so that
there was no change in the basic composition except for formic
acid. Results of compositional analysis at the start of the
experiment, and the formic acid concentration at the completion of
the experiment are shown in the table below.
Example 18
[0128] The same experiment as in Comparative Example 6 was
conducted except that H.sub.2, CO.sub.2, and CO were fed to the
autoclave to make a H.sub.2 partial pressure of 1.2 kPa (absolute
pressure), a CO.sub.2 partial pressure of 0.5 kPa (absolute
pressure), and a CO partial pressure of 0.004 MPa (absolute
pressure). After cooling, the liquid was sampled and subjected to
compositional analysis. As a result, the formic acid concentration
was 38 ppm. The MA concentration was 1.0% and was thus hardly
changed. There was no large change in the composition of the other
components. Results of compositional analysis at the start of the
experiment, and the formic acid concentration at the completion of
the experiment are shown in the table below.
[0129] The conditions and results of Comparative Examples and
Examples are shown in Tables 1 and 2. In Tables 1 and 2, "PH2"
represents a hydrogen partial pressure, "PCO2" represents a carbon
dioxide partial pressure, and "PCO" represents a carbon monoxide
partial pressure. In the tables, "balance" is described about the
acetic acid concentration. In actuality, the sampled solution may
contain 1 ppm to 1% in total of impurities such as by-products
mentioned in the section described about the reaction mixture.
TABLE-US-00001 TABLE 1 Potas- Acetic sium anhy- Propionic Acetic
Temper- Pres- acetate dride acid acid ature sure wt % wt % wt % wt
% .degree. C. kPaG Comparative 0 0 92.1 7.9 165.2 131 Example 1
Comparative 0 0 0 100 165.1 255 Example 2 Example 1 0 0 91.8 8.2
160.5 93 Example 2 0 0 0 100 160.2 217 Example 3 34.1 0 0 65.9
155.1 91 Example 4 0 91.1 0 8.9 154.8 89 Example 5 0 0 75.3 24.7
155.3 90 Example 6 0 0 0 100 155.1 181 Example 7 23.2 0 0 76.8
150.5 92 Example 8 0 74.3 0 25.7 150.3 90 Example 9 0 0 55.4 44.6
150.9 93 Example 10 0 0 0 100 150 147 Example 11 12.6 0 0 87.4
144.3 88 Example 12 0 44.8 0 55.2 144.7 90 Example 13 0 0 29 71
144.6 91 Example 14 0 0 0 100 145.2 117 Example 15 0 0 0 100 140.1
90
TABLE-US-00002 TABLE 2 Results of corrosion test Zr HB2 HC276
SUS316 mm/y mm/y mm/y mm/y Comparative 0.000 0.05 0.12 0.22 Example
1 Comparative 0.000 0.05 0.12 0.21 Example 2 Example 1 0.000 0.04
0.082 0.17 Example 2 0.000 0.04 0.081 0.15 Example 3 0.000 0.028
0.049 0.105 Example 4 0.000 0.03 0.05 0.113 Example 5 0.000 0.029
0.051 0.095 Example 6 0.000 0.027 0.048 0.092 Example 7 0.000 0.020
0.030 0.049 Example 8 0.000 0.020 0.034 0.053 Example 9 0.000 0.021
0.033 0.051 Example 10 0.000 0.019 0.03 0.030 Example 11 0.000
0.009 0.018 0.031 Example 12 0.000 0.008 0.016 0.029 Example 13
0.000 0.008 0.015 0.023 Example 14 0.000 0.007 0.013 0.025 Example
15 0.000 0.000 0.005 0.011
[Discussion on Results]
[0130] From Comparative Example 1 and Examples 1 to 3, it is
evident that at lower H.sub.2 and CO.sub.2 partial pressures, the
amount of formic acid formed is smaller, and formic acid is formed
substantially in proportion to the H.sub.2 and CO.sub.2 partial
pressures.
[0131] From Comparative Examples 1 and 2 and Example 4, it is
evident that at a higher temperature, formic acid formation is
suppressed.
[0132] From Comparative Example 3 and Examples 5 and 8, it is
evident that at a higher temperature, the decomposition of formic
acid is promoted even under conditions different from the
composition of Comparative Example 1.
[0133] From Comparative Example 4 and Examples 6 and 9, it is
evident that at a higher temperature, the decomposition of formic
acid is promoted even under conditions different from the
composition of Comparative Example 1.
[0134] From Comparative Example 5 and Examples 7 and 10, it is
evident that at a higher temperature, the decomposition of formic
acid is promoted even under conditions different from the
composition of Comparative Example 1.
[0135] From Examples 11 and 12, it is evident that at a higher
temperature, the decomposition of formic acid is promoted even
under conditions different from the composition of Comparative
Example 1.
[0136] From Examples 12 and 13, it is evident that even the absence
of CO hardly influence a formic acid decomposition rate.
[0137] Although Examples 14 and 12 differ somewhat in composition,
it is evident that under high temperature conditions, the
decomposition of formic acid is similarly promoted.
[0138] From Examples 8 and 15, it is evident that the decomposition
of formic acid is promoted as the H.sub.2 and CO.sub.2 partial
pressures are reduced.
[0139] From Examples 15 to 17, it is evident that at a longer
retention time, the decomposition of formic acid is promoted.
[0140] From Comparative Example 6 and Example 18, it is evident
that the decomposition of formic acid is promoted as the H.sub.2
and CO.sub.2 partial pressures are reduced.
[0141] Specifically, the present invention relates to the
following:
[0142] Appendix 1: A method for producing acetic acid, comprising
at least one step selected from a step that satisfies the following
operating conditions (i) and a step that satisfies the following
operating conditions (ii) in an acetic acid production process:
[0143] (i) operating conditions involving a hydrogen partial
pressure of less than 500 kPa (absolute pressure), a carbon dioxide
partial pressure of less than 70 kPa (absolute pressure), and an
operating temperature of more than 175.degree. C.; and
[0144] (ii) operating conditions involving a hydrogen partial
pressure of not more than 5 kPa (absolute pressure), a carbon
dioxide partial pressure of less than 20 kPa (absolute pressure),
and an operating temperature of more than 100.degree. C.
[0145] Appendix 2: The method for producing acetic acid according
to appendix 1, wherein the operating conditions (i) involve a
hydrogen partial pressure (absolute pressure) of not more than 400
kPa (preferably not more than 300 kPa, more preferably not more
than 200 kPa, further preferably not more than 150 kPa).
[0146] Appendix 3: The method for producing acetic acid according
to appendix 1 or 2, wherein the operating conditions (i) involve a
hydrogen partial pressure (absolute pressure) of more than 1 kPa
(or more than 5 kPa).
[0147] Appendix 4: The method for producing acetic acid according
to any one of appendixes 1 to 3, wherein the operating conditions
(i) involve a carbon dioxide partial pressure (absolute pressure)
of not more than 60 kPa (preferably not more than 50 kPa, more
preferably not more than 40 kPa, further preferably not more than
30 kPa).
[0148] Appendix 5: The method for producing acetic acid according
to any one of appendixes 1 to 4, wherein the operating conditions
(i) involve a carbon dioxide partial pressure (absolute pressure)
of not less than 2 kPa (or not less than 20 kPa).
[0149] Appendix 6: The method for producing acetic acid according
to any one of appendixes 1 to 5, wherein the operating conditions
(i) involve an operating temperature of not less than 178.degree.
C. (preferably not less than 181.degree. C., more preferably not
less than 184.degree. C.).
[0150] Appendix 7: The method for producing acetic acid according
to any one of appendixes 1 to 6, wherein the operating conditions
(i) involve an operating temperature of not more than 250.degree.
C. (preferably not more than 230.degree. C., more preferably not
more than 200.degree. C.).
[0151] Appendix 8: The method for producing acetic acid according
to any one of appendixes 1 to 7, wherein the operating conditions
(ii) involve a hydrogen partial pressure (absolute pressure) of not
more than 4 kPa (preferably not more than 3 kPa, more preferably
not more than 2 kPa, further preferably not more than 1 kPa).
[0152] Appendix 9: The method for producing acetic acid according
to any one of appendixes 1 to 8, wherein the operating conditions
(ii) involve a carbon dioxide partial pressure (absolute pressure)
of not more than 18 kPa (preferably not more than 16 kPa, more
preferably not more than 14 kPa, further preferably not more than
12 kPa).
[0153] Appendix 10: The method for producing acetic acid according
to any one of appendixes 1 to 9, wherein the operating conditions
(ii) involve an operating temperature of not less than 102.degree.
C. (preferably not less than 104.degree. C., more preferably not
less than 106.degree. C., further preferably not less than
112.degree. C.).
[0154] Appendix 11: The method for producing acetic acid according
to any one of appendixes 1 to 10, wherein the operating conditions
(ii) involve an operating temperature of not more than 250.degree.
C. (preferably not more than 200.degree. C., more preferably not
more than 175.degree. C.).
[0155] Appendix 12: The method for producing acetic acid according
to any one of appendixes 1 to 11, wherein the operating conditions
(ii) involve a hydrogen partial pressure of not more than 1 kPa
(absolute pressure) and a carbon dioxide partial pressure of less
than 2 kPa (absolute pressure).
[0156] Appendix 13: The method for producing acetic acid according
to appendix 12, wherein the operating conditions (ii) involve a
hydrogen partial pressure (absolute pressure) of not more than 0.9
kPa (preferably not more than 0.8 kPa).
[0157] Appendix 14: The method for producing acetic acid according
to appendix 12 or 13, wherein the operating conditions (ii) involve
a carbon dioxide partial pressure (absolute pressure) of not more
than 1.8 kPa (preferably not more than 1.5 kPa, more preferably not
more than 1.0 kPa, further preferably not more than 0.5 kPa).
[0158] Appendix 15: The method for producing acetic acid according
to any one of appendixes 1 to 14, wherein the method has a reaction
step that satisfies the operating conditions (i).
[0159] Appendix 16: The method for producing acetic acid according
to appendix 15, wherein a reaction mixture liquid in the reaction
step has an acetic acid concentration of not less than 30% by mass
(e.g., 30 to 90% by mass) and a formic acid concentration of not
more than 102 ppm by mass (e.g., 0 to 102 ppm by mass).
[0160] Appendix 17: The method for producing acetic acid according
to appendix 15 or 16, wherein a reaction mixture liquid in the
reaction step has an acetic acid concentration of 50 to 90% by mass
(e.g., 60 to 80% by mass), a metal catalyst concentration (in terms
of the metal) of 200 to 10000 ppm by mass (e.g., 200 to 5000 ppm by
mass, preferably 400 to 2000 ppm by mass), a methyl iodide
concentration of 1 to 20% by mass (e.g., 5 to 15% by mass), an
ionic iodide concentration of 1 to 25% by mass (e.g., 5 to 20% by
mass), a water concentration of 0.1 to 15% by mass (e.g., 0.8 to
10% by mass), a methyl acetate concentration of 0.1 to 30% by mass
(e.g., 1 to 10% by mass), and a formic acid concentration of not
more than 102 ppm by mass (e.g., not more than 85 ppm by mass).
[0161] Appendix 18: The method for producing acetic acid according
to any one of appendixes 15 to 17, wherein the reaction mixture in
the reaction step has a formic acid concentration of 0 to 102 ppm
by mass (preferably 0 to 85 ppm by mass, more preferably 0 to 50
ppm by mass).
[0162] Appendix 19: The method for producing acetic acid according
to any one of appendixes 1 to 18, wherein the method has an
evaporation step or a distillation step that satisfies the
operating conditions (ii).
[0163] Appendix 20: The method for producing acetic acid according
to appendix 19, wherein a charging mixture for an evaporator in the
evaporation step has an acetic acid concentration of 50 to 90% by
mass (e.g., 60 to 80% by mass), a metal catalyst concentration (in
terms of the metal) of 200 to 10000 ppm by mass (e.g., 200 to 5000
ppm by mass, preferably 400 to 2000 ppm by mass), a methyl iodide
concentration of 1 to 20% by mass (e.g., 5 to 15% by mass), an
ionic iodide concentration of 1 to 25% by mass (e.g., 5 to 20% by
mass), a water concentration of 0.1 to 15% by mass (e.g., 0.8 to
10% by mass), a methyl acetate concentration of 0.1 to 30% by mass
(e.g., 1 to 10% by mass), a formic acid concentration of not more
than 10000 ppm by mass (e.g., 0 to 1000 ppm by mass, preferably 10
to 500 ppm by mass, further preferably 15 to 200 ppm by mass,
particularly preferably 20 to 100 ppm by mass).
[0164] Appendix 21: The method for producing acetic acid according
to appendix 19, wherein a charging mixture for a distillation
column in the distillation step has an acetic acid concentration of
not less than 30% by mass (e.g., 30 to 99.999% by mass) and a
formic acid concentration of not less than 5 ppm by mass (e.g., 5
to 10000 ppm by mass).
[0165] Appendix 22: The method for producing acetic acid according
to appendix 19, wherein a charging mixture for a distillation
column in the distillation step has an acetic acid concentration of
40 to 85% by mass (e.g., 50 to 75% by mass), a methyl iodide
concentration of 2 to 50% by mass (e.g., 5 to 30% by mass), a water
concentration of 0.2 to 20% by mass (e.g., 1 to 15% by mass), a
methyl acetate concentration of 0.2 to 50% by mass (e.g., 2 to 30%
by mass), and a formic acid concentration of 5 to 10000 ppm by mass
(e.g., 10 to 1000 ppm by mass, preferably 10 to 500 ppm by mass,
further preferably 15 to 200 ppm by mass, particularly preferably
20 to 100 ppm by mass).
[0166] Appendix 23: The method for producing acetic acid according
to appendix 19, wherein a charging mixture for a distillation
column in the distillation step has an acetic acid concentration of
80 to 99.9% by mass (e.g., 90 to 99.9% by mass, preferably 93 to
99% by mass), a methyl iodide concentration of 0.01 to 16% by mass
(e.g., 0.1 to 8% by mass, preferably 0.2 to 5% by mass), a water
concentration of 0.05 to 18% by mass (e.g., 0.1 to 8% by mass,
preferably 0.2 to 5% by mass), a methyl acetate concentration of
0.01 to 16% by mass (e.g., 0.1 to 8% by mass, preferably 0.2 to 5%
by mass), and a formic acid concentration of 5 to 10000 ppm by mass
(e.g., 10 to 1000 ppm by mass, preferably 10 to 500 ppm by mass,
further preferably 15 to 200 ppm by mass, particularly preferably
20 to 100 ppm by mass).
[0167] Appendix 24: The method for producing acetic acid according
to appendix 19, wherein a charging mixture for a distillation
column in the distillation step has an acetic acid concentration of
99.1 to 99.999% by mass and a formic acid concentration of 5 to
9000 ppm by mass (e.g., 10 to 1000 ppm by mass, preferably 10 to
500 ppm by mass, further preferably 15 to 200 ppm by mass,
particularly preferably 20 to 100 ppm by mass).
[0168] Appendix 25: The method for producing acetic acid according
to any one of appendixes 1 to 24, wherein the acetic acid
production process has a carbonylation reaction step of reacting
methanol with carbon monoxide to produce acetic acid, an
evaporation step of separating the reaction mixture obtained in the
carbonylation reaction step into a vapor stream and a residual
liquid stream, and a lower boiling point component removal step of
separating the vapor stream by distillation into an overhead stream
rich in lower boiling point component and a first acetic acid
stream rich in acetic acid, or
[0169] wherein the acetic acid production process further has at
least one of the following steps (a)-(d) in addition to the
carbonylation reaction step, the evaporation step, and the lower
boiling point component removal step:
(a) a dehydration step of separating the first acetic acid stream
by distillation into an overhead stream rich in water and a second
acetic acid stream more enriched with acetic acid than the first
acetic acid stream, (b) a higher boiling point component removal
step of separating the first acetic acid stream or the second
acetic acid stream by distillation into a bottom stream rich in
higher boiling point component and a third acetic acid stream more
enriched with acetic acid than the acetic acid stream before the
distillation, (c) an adsorptive removal step of treating the first
acetic acid stream, the second acetic acid stream, or the third
acetic acid stream with an ion exchange resin to obtain a fourth
acetic acid stream, and (d) a product step of distilling the first
acetic acid stream, the second acetic acid stream, the third acetic
acid stream or the fourth acetic acid stream to obtain a fifth
acetic acid stream more enriched with acetic acid than the acetic
acid stream before the distillation.
[0170] Appendix 26: The method for producing acetic acid according
to appendix 25, wherein the carbonylation reaction step satisfies
the operating conditions (i).
[0171] Appendix 27: The method for producing acetic acid according
to appendix 25 or 26, wherein at least one step selected from the
evaporation step, the lower boiling point component removal step,
the dehydration step, the higher boiling point component removal
step, and the product step satisfies the operating conditions
(ii).
[0172] Appendix 28: The method for producing acetic acid according
to any one of appendixes 25 to 27, wherein the evaporation step
satisfies the operating conditions (ii).
[0173] Appendix 29: The method for producing acetic acid according
to appendix 28, wherein the operating conditions (ii) satisfied by
the evaporation step involve a hydrogen partial pressure (absolute
pressure) of not more than 4 kPa (preferably not more than 3 kPa,
more preferably not more than 1 kPa, further preferably not more
than 0.8 kPa).
[0174] Appendix 30: The method for producing acetic acid according
to appendix 28 or 29, wherein the operating conditions (ii)
satisfied by the evaporation step involve a carbon dioxide partial
pressure (absolute pressure) of not more than 12 kPa (preferably
not more than 8 kPa, more preferably not more than 3 kPa, further
preferably not more than 1 kPa).
[0175] Appendix 31: The method for producing acetic acid according
to any one of appendixes 28 to 30, wherein the operating conditions
(ii) satisfied by the evaporation step involve an operating
temperature of not less than 112.degree. C. (preferably not less
than 120.degree. C., more preferably not less than 130.degree. C.;
the upper limit is, for example, 260.degree. C., preferably
200.degree. C., more preferably 180.degree. C. (or 170.degree. C.
or 160.degree. C.)).
[0176] Appendix 32: The method for producing acetic acid according
to any one of appendixes 25 to 31, wherein the lower boiling point
component removal step satisfies the operating conditions (ii).
[0177] Appendix 33: The method for producing acetic acid according
to appendix 32, wherein the operating conditions (ii) satisfied by
the lower boiling point component removal step involve a hydrogen
partial pressure (absolute pressure) of not more than 4 kPa
(preferably not more than 3 kPa, more preferably not more than 1
kPa).
[0178] Appendix 34: The method for producing acetic acid according
to appendix 32 or 33, wherein the operating conditions (ii)
satisfied by the lower boiling point component removal step involve
a carbon dioxide partial pressure (absolute pressure) of not more
than 12 kPa (preferably not more than 8 kPa, more preferably not
more than 3 kPa, further preferably not more than 1 kPa).
[0179] Appendix 35: The method for producing acetic acid according
to any one of appendixes 32 to 34, wherein the operating conditions
(ii) satisfied by the lower boiling point component removal step
involve an operating temperature of not less than 112.degree. C.
(preferably not less than 114.degree. C.; the upper limit is, for
example, 165.degree. C., preferably 160.degree. C., more preferably
150.degree. C. (or 140.degree. C. or 130.degree. C.)).
[0180] Appendix 36: The method for producing acetic acid according
to any one of appendixes 32 to 35, wherein a charging mixture for a
distillation column in the lower boiling point component removal
step has an acetic acid concentration of not less than 30% by mass
(e.g., 30 to 99.999% by mass) and a formic acid concentration of
not less than 5 ppm by mass (e.g., 5 to 10000 ppm by mass).
[0181] Appendix 37: The method for producing acetic acid according
to any one of appendixes 32 to 35, wherein a charging mixture for a
distillation column in the lower boiling point component removal
step has an acetic acid concentration of 40 to 85% by mass (e.g.,
50 to 85% by mass, preferably 50 to 75% by mass, more preferably 55
to 75% by mass), a methyl iodide concentration of 2 to 50% by mass
(e.g., 5 to 30% by mass), a water concentration of 0.2 to 20% by
mass (e.g., 1 to 15% by mass), a methyl acetate concentration of
0.2 to 50% by mass (e.g., 2 to 30% by mass), and a formic acid
concentration of 5 to 10000 ppm by mass (e.g., 10 to 1000 ppm by
mass, more preferably 10 to 500 ppm by mass, particularly, 15 to
200 ppm by mass, in particular, 20 to 100 ppm by mass).
[0182] Appendix 38: The method for producing acetic acid according
to any one of appendixes 25 to 37, wherein the dehydration step
satisfies the operating conditions (ii).
[0183] Appendix 39: The method for producing acetic acid according
to appendix 38, wherein the operating conditions (ii) satisfied by
the dehydration step involve a hydrogen partial pressure (absolute
pressure) of not more than 2 kPa (preferably not more than 1 kPa,
more preferably not more than 0.5 kPa).
[0184] Appendix 40: The method for producing acetic acid according
to appendix 38 or 39, wherein the operating conditions (ii)
satisfied by the dehydration step involve a carbon dioxide partial
pressure (absolute pressure) of not more than 5 kPa (preferably not
more than 2 kPa, more preferably not more than 1 kPa, further
preferably not more than 0.5 kPa).
[0185] Appendix 41: The method for producing acetic acid according
to any one of appendixes 38 to 40, wherein the operating conditions
(ii) satisfied by the dehydration step involve an operating
temperature of not less than 120.degree. C. (preferably not less
than 130.degree. C.; the upper limit is, for example, 170.degree.
C., preferably 165.degree. C., more preferably 160.degree. C.,
further preferably 155.degree. C.).
[0186] Appendix 42: The method for producing acetic acid according
to any one of appendixes 38 to 41, wherein a charging mixture for a
distillation column in the dehydration step has an acetic acid
concentration of not less than 30% by mass (e.g., 30 to 99.999% by
mass) and a formic acid concentration of not less than 5 ppm by
mass (e.g., 5 to 10000 ppm by mass).
[0187] Appendix 43: The method for producing acetic acid according
to any one of appendixes 38 to 41, wherein a charging mixture for a
distillation column in the dehydration step has an acetic acid
concentration of 80 to 99.9% by mass (e.g., 90 to 99.9% by mass,
particularly, 93 to 99% by mass), a methyl iodide concentration of
0.01 to 16% by mass (e.g., 0.1 to 8% by mass, particularly, 0.2 to
5% by mass), a water concentration of 0.05 to 18% by mass (e.g.,
0.1 to 8% by mass, particularly, 0.2 to 5% by mass), a methyl
acetate concentration of 0.01 to 16% by mass (e.g., 0.1 to 8% by
mass, particularly, 0.2 to 5% by mass), and a formic acid
concentration of 5 to 10000 ppm by mass (e.g., 10 to 1000 ppm by
mass, more preferably 10 to 500 ppm by mass, particularly, 15 to
200 ppm by mass, in particular, 20 to 100 ppm by mass).
[0188] Appendix 44: The method for producing acetic acid according
to any one of appendixes 25 to 43, wherein the higher boiling point
component removal step satisfies the operating conditions (ii).
[0189] Appendix 45: The method for producing acetic acid according
to appendix 44, wherein the operating conditions (ii) satisfied by
the higher boiling point component removal step involve a hydrogen
partial pressure (absolute pressure) of not more than 2 kPa
(preferably not more than 1 kPa, more preferably not more than 0.5
kPa).
[0190] Appendix 46: The method for producing acetic acid according
to appendix 44 or 45, wherein the operating conditions (ii)
satisfied by the higher boiling point component removal step
involve a carbon dioxide partial pressure (absolute pressure) of
not more than 5 kPa (preferably not more than 2 kPa, more
preferably not more than 1 kPa, further preferably not more than
0.5 kPa).
[0191] Appendix 47: The method for producing acetic acid according
to any one of appendixes 44 to 46, wherein the operating conditions
(ii) satisfied by the higher boiling point component removal step
involve an operating temperature of not less than 120.degree. C.
(preferably not less than 130.degree. C.; the upper limit is, for
example, 165.degree. C., preferably 160.degree. C., further
preferably 155.degree. C.).
[0192] Appendix 48: The method for producing acetic acid according
to any one of appendixes 44 to 47, wherein a charging mixture for a
distillation column in the higher boiling point component removal
step has an acetic acid concentration of 99.1 to 99.99% by mass and
a formic acid concentration of 5 to 9000 ppm by mass (e.g., 10 to
1000 ppm by mass, more preferably 10 to 500 ppm by mass,
particularly, 15 to 200 ppm by mass, in particular, 20 to 100 ppm
by mass).
[0193] Appendix 49: The method for producing acetic acid according
to any one of appendixes 25 to 48, wherein the product step
satisfies the operating conditions (ii).
[0194] Appendix 50: The method for producing acetic acid according
to appendix 49, wherein the operating conditions (ii) satisfied by
the product step involve a hydrogen partial pressure (absolute
pressure) of not more than 2 kPa (preferably not more than 1 kPa,
more preferably not more than 0.5 kPa).
[0195] Appendix 51: The method for producing acetic acid according
to appendix 49 or 50, wherein the operating conditions (ii)
satisfied by the product step involve a carbon dioxide partial
pressure (absolute pressure) of not more than 5 kPa (preferably not
more than 2 kPa, more preferably not more than 1 kPa, further
preferably not more than 0.5 kPa).
[0196] Appendix 52: The method for producing acetic acid according
to any one of appendixes 49 to 51, wherein the operating conditions
(ii) satisfied by the product step involve an operating temperature
of not less than 120.degree. C. (preferably not less than
130.degree. C.; the upper limit is, for example, 165.degree. C.,
preferably 160.degree. C., more preferably 155.degree. C.).
[0197] Appendix 53: The method for producing acetic acid according
to any one of appendixes 49 to 52, wherein a charging mixture for a
product column in the product step has an acetic acid concentration
of 99.8 to 99.999% by mass and a formic acid concentration of 5 to
2000 ppm by mass (e.g., 5 to 1000 ppm by mass, particularly, 5 to
100 ppm by mass).
[0198] Appendix 54: The method for producing acetic acid according
to any one of appendixes 1 to 53, wherein a retention time in the
step that satisfies the operating conditions (i) or the step that
satisfies the operating conditions (ii) is not less than 1 minute
(e.g., not less than 5 minutes, particularly, not less than 10
minutes).
[0199] Appendix 55: The method for producing acetic acid according
to appendix 54, wherein the retention time in the step that
satisfies the operating conditions (i) or the step that satisfies
the operating conditions (ii) is not more than 2 hours (preferably
not more than 1 hour).
[0200] Appendix 56: The method for producing acetic acid according
to any one of appendixes 1 to 55, wherein a process solution having
a formic acid concentration of not less than 10 ppm by mass (e.g.,
10 to 10000 ppm by mass, preferably 15 to 1000 ppm by mass, further
preferably 20 to 200 ppm by mass) is recycled to a step that
satisfies (iii) operating conditions involving a hydrogen partial
pressure of less than 500 kPa (absolute pressure), a carbon dioxide
partial pressure of less than 70 kPa (absolute pressure), and an
operating temperature of more than 100.degree. C.
[0201] Appendix 57: The method for producing acetic acid according
to any one of appendixes 1 to 56, wherein the acetic acid
production process has at least one distillation step, and a column
top fraction of a distillation column in the at least one
distillation step is recycled to the step that satisfies the
operating conditions (i) and/or the step that satisfies the
operating conditions (ii).
[0202] Appendix 58: The method for producing acetic acid according
to appendix 57, wherein the step to which the column top fraction
of a distillation column is recycled is the reaction step and/or
the evaporation step or a distillation step positioned upstream
from the distillation step associated with the distillation
column.
[0203] Appendix 59: The method for producing acetic acid according
to appendix 57 or 58, wherein the step that satisfies the operating
conditions (iii) is at least one step selected from the reaction
step, the evaporation step, the lower boiling point component
removal step, and the dehydration step.
INDUSTRIAL APPLICABILITY
[0204] The method for producing acetic acid of the present
invention can be used as industrial method for producing acetic
acid by carbonylation process of a methanol method (acetic acid
process of a methanol method).
REFERENCE SIGNS LIST
[0205] 1: reaction vessel [0206] 2: evaporator [0207] 3, 5, and 6:
distillation column [0208] 4: decanter [0209] 7: ion exchange resin
column [0210] 8: scrubber system [0211] 9: acetaldehyde separation
and removal system [0212] 16: reaction mixture feed line [0213] 17:
vapor stream discharge line [0214] 18 and 19: residual liquid
stream recycle line [0215] 54: carbon monoxide-containing gas
introduction line [0216] 55 and 56: potassium hydroxide
introduction line [0217] 57: catalyst circulating pump [0218] 91:
distillation column (first acetaldehyde removal column) [0219] 92:
extraction column [0220] 93: distillation column (second
acetaldehyde removal column) [0221] 94: distillation column
(extractive distillation column) [0222] 95: decanter [0223] 96:
decanter [0224] 97: distillation column (acetaldehyde removal
column) [0225] 98: distillation column (extractive distillation
column) [0226] 99: decanter [0227] 200: chimney tray
* * * * *